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CRETACEOUS SYSTEM
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CRETACEOUS See also:SYSTEM , in See also:geology, the See also:group of stratified rocks which normally occupy a position above the See also:Jurassic system and below the See also:oldest See also:Tertiary deposits; therefore it is in this system that the closing records of the See also:great Mesozoic era are to be found. The name furnishes an excellent See also:illustration of the inconvenience of employing a See also:local lithological feature in the descriptive See also:title of a wide-ranging See also:rock-system. The See also: C. Chamberlin and R. D. See also:Salisbury to show the See also:main subdivisions of the See also:North See also:American Cretaceous rocks. The correlation of the See also:minor subdivisions of Europe and See also:America are only approximate. Relation of the Cretaceous Strata to the Systems above and below. —In central and See also:northern Europe the boundary between the Cretaceous and Tertiary strata is sharply defined by a fairly general unconformity, except in the Danian and Montian beds, where there is a certain commingling of Tertiary with Cretaceous fossils. The relations with the underlying Jurassic rocks are not so clearly defined, partly because the earliest Cretaceous rocks are obscured by too great a thickness of younger strata, and partly because the lowest observable rocks of the system are not the oldest, but are higher members of the system that have overlapped on to much older rocks. However, in the See also:south of See also:England, in the Alpine area, and in See also:part of N.W. See also:Germany the passage from Jurassic to Cretaceous is so See also:gradual that there is some divergence of See also:opinion as to the best position for the See also:line of separation. In the Alpine region this passage is formed by marine beds, in the other two by brackish-See also:water deposits. In a like manner the See also:Potomac beds of N. America grade downwards into the Jurassic; while in the See also:Laramie formation an upward passage is observed into the See also:Eocene deposits. There is a very general unconformity and break between the Lower and Upper Cretaceous; this has led Chamberlin and Salisbury to suggest that the Lower Cretaceous should be regarded as a See also:separate See also:period with the title " Comanchean." Physiographical Conditions and Types of See also:Deposit.—With the opening of the Cretaceous in Europe there commenced a period of marine transgression; in the central and western See also:European region this took place from the S. towards the N., slow at first and local in effect, but becoming more decided at the beginning of the upper See also:division. During the earlier portion of the period, S. England, See also:Belgium and See also:Hanover were covered by a great See also:series of estuarine sands and See also:clays, termed the See also:Wealden formation (q.v.), the See also:delta of a large See also:river or See also:rivers flowing probably from the N.W. Meanwhile, in the See also:rest of Europe alternations of marine and estuarine deposits were being laid down; but over the Alpine region See also:lay the open See also:sea, where there flourished See also:coral reefs and great See also:banks of clam-like molluscs. The sea gradually encroached upon the estuarine Wealden area, and at the See also:time of the See also:Aptian deposits See also:uniform marine conditions prevailed from western Europe through See also:Russia into See also:Asia. This See also:extension of the sea is illustrated in England by the overlap o1 the See also:Gault over the Lower See also:Greensand on to the older rocks, and by similar occurrences in N. See also:France and Germany. Almost throughout the Upper Cretaceous period the marine invasion continued, varied here and there by slight movements in the opposite sense which did not, however, interfere with the quiet general advance of the sea. This marine extension made itself See also:felt over the old central See also:plateau of France, the N. of Great Britain, the See also:Spanish See also:peninsula, the Armorican peninsula, and also in the Bavarian See also:Jura and Bohemia; it affected the northern part of See also:Africa and See also:East Africa; in N. America the sea spread over the entire length of the Rocky See also:Mountain region; and in See also:Brazil, eastern Asia and western See also:Australia, Upper Cretaceous deposits are found resting directly upon much older rocks. Indeed, at this time there happened one of the greatest changes in the See also:distribution of See also:land and water that have been recorded in See also:geological See also:history. We have seen that in See also:early Cretaceous times marine limestones were being formed in See also:southern Europe, while estuarine sands and muds were being laid down in the Anglo-See also:German delta, and that beds of intermediate See also:character were being made in parts of N. France and Germany. During later Cretaceous times this striking difference between the northern and southern facies was maintained, notwithstanding the fact that the later deposits were of marine origin in both regions. In the northern region the gradual deepening and accompanying extension of the sea caused the sandy deposits to become finer grained in N.W. Europe. The sandy beds and clays then gave way to marly deposits, and in these early stages glauconitic grains are very characteristically See also:present both in the See also:sand and in the marls. In their turn these marly deposits in the Anglo-Parisian basin were succeeded gradually and somewhat intermittently by the purer, soft See also:lime-See also: In the north, the genera Inoceramus and Belemnitella are particularly abundant. In the south, the remarkable, large, clam-like, aberrant pelecypods, the Hippuritidae, Rudistes, Caprotina, &c., attained an extraordinary development; they See also:form great lenticular banks, like the clam banks of warm seas, or like our See also:modern See also:oyster-beds; they appear in successive species in the different stages of the Cretaceous system of the south, and can be used for marking palaeontological horizons as the cephalopods are used elsewhere. Certain genera of See also:ammonites, Haploceras, Lytoceras, Phylloceras, rare in the north, are See also:common in the south; and the southern facies is further characterized by the peculiar group of swollen belemnites (Dumontia), by the gasteropods Actionella, Nerinea, &c., and by See also:reef-See also:building See also:corals. The southern facies is far more widespread and typical of the period than is the chalk; it not only covers all southern Europe, but spreads eastwards far into Asia and See also:round the Mediterranean basin into Africa. It is found again in See also:Texas, See also:Alabama, See also:Mexico, the See also:West Indies and See also:Colombia; though limestones of the chalk type are found in Texas, New See also:Zealand, and locally in one or two other places. The marine deposits are organically formed limestones, in which See also:foraminifera and large bivalve See also:mollusca See also:play a leading part, marls and sandstones; See also:dolomite and oolitic and pisolitic limestones are also known. The Cretaceous seas were probably comparatively shallow; Distribution of Cretaceous Rocks n •ees-/n which C/tle. CoOtoceo s rheoComlon) Rocs Ore Lnown. .. .ouage. .. ,to,e se.onlen) .. .. .. C.elooeo/s Rocks urtxnOwn 0, ooseot ossh/e O orots %on of IocO A See — 0/der /See also:nye. a b European Classification. . a Britain. Germany, &c., several a N 5 .11 other parts of Europe. Stages. Sub-stages. r b a ; z an L Montian. (placed by some in MarlsandpisoliticLime- ai y the Tertiary). stone of See also:Meudon. o ro o 3 See also:Limestone of Saltholm'~o Danian. Chalk of See also:Trim- 3 Ej - Maestrichtian (Dor- See also:ingham. and Faxo (Den.See also:mark).~ vi a ro .~ donian). Upper Chalk with aro o " CI) U v ro v a Aturian. Flints. Upper Quader Sand- o Q v °o a .0 Campanian. stone. Q A a C C o °u Santonian. Quader Marls and;o o v 8 a) 0 c L. U Emscherian. Coniacian. Planer Marls. c :e'8'' 5 .- m 0 a b '•. G. .ro See also:Middle Chalk with- b ro E. Angoumian. out Flints. Upper Planer. > o La - ° vi N Turonian. ° '~ d ° Ligerian. a c o -a v) ro P= v; -o ~ o ~.yAw, m ro o Carentonian. See also:Grey Chalk. L r. Planer and L r. a o as ro .5 c C7 Cenomanian. Chalk See also:marl. Quader. t ro '6 ro'= . Rothomagian. See also:Cambridge See also:Green- °, v v y sand. oUU» l .N. n (n Tourtia of See also:Mons, &c. w • ° = = c v ..... o ............ ro c Gault and Upper Greensand. ° ° See also:Albian. Gault. Flammen See also:merge!. See also:Clay o n of N. Germany. . Gargasian. Urgonian a -o o ° Aptian. Lower Greensand. Requienia . ro Bedoulian. (caprotina) See also:Kalk ° m o Barremian. See also:Weald Clay or Schrattenkalk. L.) .a o a Hauterivian. and pa ~_ U Neocomian. Valangian. See also:Hastings sands. o 3 0 3 Berriasian. a o •o ° L. -a ° a a u 0. a 41'~ .: n vi y o a v o . ro LS, a1 •,' O a 0 c U a n o -a a ro q 3 o as G or, 'O OU ~C! v U C7 U U ro ro •ir +, a E :r U bbe .4 z d O G4 E-H P.. E. Montian from Danian Aturian Maestrichtian Campanian Emscherian Santonian Coniacian Senonian , Turonian Angoumian Ligerian Cenomanian Carentonian Rothomagian Albian Selbornian Aptian Gargasian Bedoulian Barremian Hauterivian Valengian Neocomian Berriasian Urgonian See also:Note to Table. Mons in Belgium. Denmark = Garumnien of Leymerie. See also:Adour. Maestricht. See also:Champagne. Emscher river in See also:Westphalia. See also:Saintonge. See also:Cognac. See also:Sens in See also:department of See also:Yonne. See also:Touraine. See also:Angoumois. the See also:Loire. Le Mans (Cenomanum). See also:Charente. See also:Rouen (Rothomagus). dept. of See also:Aube. See also:Selborne in See also:Hampshire. See also:Apt in See also:Vaucluse. Gargas near Apt. la Bedoule (See also:Var) = Rhodanien of See also:Renevier. Barreme in Basses Alpes. Hauterive on See also:Lake of See also:Neuchatel. See also:Chateau de Valengin near Neuchatel. Neuchatel (Neocomum). Berrias (See also:Ardeche) near Besseges. Orgon near See also:Arles. this was certainly the See also:case where the deposits are sandy, and in the regions occupied by the hippuritic See also:fauna. Much discussion has taken place as to the See also:depth of the chalk sea. Stress has been laid upon the resemblance of this deposit to the modern deep-sea See also:globigerina-See also:ooze; but on the whole the See also:evidence is in favour of moderate depth, perhaps not more than r000 fathoms; the freedom of the deposit from detrital See also:matter being regarded as due to the See also:low See also:elevation of the surrounding land, and the main lines of drainage being in other directions. Sandy and See also:shore deposits are common throughout the system in every region. Besides the Weald, there were great lacustrine and terrestrial deposits in N. America (the Potomac, Kootenay, See also:Morrison, Dakota and Laramie formations) as well as in N. See also:Spain, and in parts of Germany, &c. The general distribution of land and sea is indicated in the See also:map. See also:Earth Movements and Vulcanicity.—During the greater part of the Cretaceous period crustal movements had been small and local in effect, but towards the See also:close a series of great deformative movements was inaugurated and continued into the next period. These movements make it possible to discriminate between the Cretaceous and Tertiary rocks, because the conditions of sedimentation were profoundly modified by them, and in most See also:Atlantic See also:Coast. Eastern Gulf Region. Western Gulf Region. Western Interior. Pacific Coast. European. ,~ Manasquan. See also:Denver, See also:Livingstone, &c.' (possibly Eocene). ...... ...... Not differ- Rancocas. Laramie. entiated or Danian. wanting. v, O See also:Ripley. See also:Montana Series. o u w 4.4 .4 See also:Monmouth. Montana Series. 2. See also:Fox Hills. Senonian. U See also:Selma. See also:Navarro. i. Fort See also:Pierre and ,, Belly River. ad Matawan. Eutaw. See also:Colorado Series. Colorado Series. Chico. Turonian. U a 2. See also:Austin. 2. Niobrara. i. See also:Eagle See also:Ford. i. See also:Benton. ...... ...... Dakota. Dakota. Cenomanian. Woodbine. Albian. Un conformity. Unconformity in places. Washita. Horsetown Aptian. 4.4 d ° See also:Tuscaloosa Series. Fredericksburg. Kootenay and Morrison d Urgonian. ~U (or See also:Como). See also:Knoxville u c Potomac Series. Neocomian. C U 4. Raritan. Wealden. 3. Patapsco. Trinity. o 2. See also:Arundel N U 0 I. Patuxent ti parts of the world there resulted a distinct break in the sequence of fossil remains. Great tracts of our modern See also:continental land areas gradually emerged, and several mountainous tracts began to be elevated, such as the Appalachians, parts of the Cordilleras, and the Rocky Mountains, and their northern continuation, and indeed the greater part of the western N. American See also:continent was intensely affected; the uplifting was associated with extensive faulting. Volcanic activity was in See also:abeyance in Europe and in much of Asia, but in America there were many eruptions and intrusions of igneous rock towards the close of the period. Diabases and peridotites had been formed during the Lower Cretaceous in the See also:San Luis Obispo region. Great masses of ash and See also:conglomerate occur in the See also:Crow's See also:Nest Pass in See also:Canada; porphyries and porphyritic tuffs of later Cretaceous age are important in the See also:Andes; while similar rocks are found in the Lower Cretaceous of New Zealand. It is, however, in the See also:Deccan See also:lava flows of See also:India that we find eruptions on a See also:scale more vast than any that have been recorded either before or since. These outpourings of lava See also:cover 200,000 sq. m. and are from 4000 to 6000 ft. thick. They See also:lie upon an eroded Cenomanian See also:surface and are to some extent interbedded with Upper Cretaceous sediments. Economic Products of Cretaceous Rocks.—Coal is one of the most important products of the rocks of this system. The principal Cretaceous See also:coal-bearing area is in the western interior of N. America, where an enormous amount of coal—mostly lignitic, but in places converted into anthracite—lies in the rocks at the See also:foot of the Rocky Mountains; most of this is of Laramie age. Similar beds occur locally •in Montana. Coal seams of Lower Cretaceous age are found in the See also:Black Hills (S. Dakota), See also:Alaska, See also:Greenland, and in New Zealand; and the " Upper Quader " of See also:Lowenberg in See also:Silesia also contains coal seams. Coals also occur in the brackish and fresh-water deposits of See also:Carinthia, See also:Dalmatia and See also:Istria, while unimportant lignitic beds are known in many other regions. The Fort Pierre beds are oil-bearing at See also:Boulder, Colorado; and the Trinity formation bears See also:asphalt and See also:bitumen. Important clay deposits are worked in the Raritan formation of New See also:Jersey, &c., and pottery clays are found in the Lowenberg See also:district in Germany. The Washita beds yield the well-known See also:hone stone. Great beds of See also:gypsum exist in the Cretaceous rocks of S. America. Near See also:Salzburg a variety of the hippuritic lime- vu. 14stone is quarried for See also:marble. Lithographic stone occurs in the See also:Pyrenees. The economic products peculiar to the chalk are mentioned in the See also:article CHALK. Beds of See also:iron ore are found in the Lower Cretaceous of Germany and England. The See also:Life of the Cretaceous Period.—The fossils from the Cretaceous series comprise marine, fresh-water and terrestrial animals and See also:plants. Foremost in See also:interest and importance is the See also:appearance in the Lower Potomac (Lower Cretaceous) of eastern and central N. America of the earliest representatives of angiospermous See also:dicotyledons, and undoubted monocotyledons, the progenitors of our modern flowering plants. The See also:angiosperms spread outward from the Atlantic coast region of N. America, and first appeared in Europe in the Aptian of See also:Portugal; towards the close of the Lower Cretaceous period they occupied parts of Greenland, the remaining land areas of N. America, and were steadily advancing in every See also:quarter of the globe. At first the Jurassic plants, the Cycads, ferns and conifers, lived on and were the dominant plant forms. Gradually, however, they took a subordinate place, and by the close of the Cretaceous period the angiosperms had gained the upper See also:hand. The earliest of these fossil angiosperms is not in a true sense a See also:primitive form, and no records of such types have yet been discovered. Some of the early forms of the Lower Cretaceous are distinctly similar to modern genera, such as Ficus, Sassafras and Aralia; others See also:bore leaves closely resembling our See also:elm, See also:maple, See also:willow, See also:oak, See also:eucalyptus, &c. Before the close of the period many other representatives of living genera had appeared, See also:beech, See also:walnut, See also:tamarisk, See also:plane, See also:laurel (Laurus), See also:cinnamon, See also:ivy, ilex, See also:viburnum, See also:buckthorn, breadfruit, oleander and others; there were also junipers, thujas, pines and sequoias and monocotyledons such as Potamogeton and Arundo. This See also:flora was widely spread and uniform; there was great similarity between that of Europe and N. America, and in parts of the See also:United States (See also:Virginia and See also:Maryland) the plants were very like those in Greenland. The general aspect of the flora was sub-tropical; the eucalyptus and other plants then common in Europe and N. America are now confined to the southern hemisphere. The marine fauna comprised foraminifera which must have swarmed in the Chalk and some of the limestone seas; their shells have formed great thickness of rock. Common forms are 12 418 the genera Alveolina, Cristellaria, Rotalia, Textularia, Orbitolina Globigerina. Radiolarians were doubtless abundant, but their remains are rare. See also:Sponges with calcareous (Peronidilla, Barroisia) and siliceous skeletons (Siphonia, Coeloptychium, Ventriculites) were very numerous in certain of the Cretaceous See also:waters. Corals were comparatively rare, Trochosmilia, Parasmilia, Holocystis being typical genera; reefs were formed in the Maestricht beds of Denmark and Faxoe, in the Neocomian and Turonian of France; in the Turonian of the See also:Alps and Pyrenees, and also in the Gosau beds and in the Utatur group of India. Sea-urchins were a conspicuous feature, and many nearly allied. forms are still living; Cidaris, Micraster, Discoidea are examples. Crinoids were represented by Marsupites, Uintacrinus and Bourgueticrinus; See also:starfish (Calliderma and Pentagonaster) were not uncommon. See also:Polyzoa were abundant; brachiopods were fairly common, though subordinate to the pelecypods; they were mostly rhynchonellids and terebratulids, which lived See also:side by side with the See also:ancient forms, like Crania and Discina. The bivalve mollusca were very important during this period, Inoceramus, Ostrea, Spondylus, Gervillia, Exogyra, Pecten, Trigonia being particularly abundant in the northern seas, while in the southern waters the remarkable Hippurites, Radiolites, Caprotina, Caprina, Mono pleura and Requienia prevailed. Gasteropods were well represented and included many modern genera. Cephalopods were important as a group, but the ammonites, so vigorous in the foregoing period, were declining and were assuming curious degenerate forms, often with a tendency to uncoil the See also:shell; Baculites, Hoplites, Turrilites, Ptychoceras, Hamites are some of the typical genera, while Belemnites and Belemnitella were abundant in the northern seas. The vertebrate fauna of the Cretaceous period differed in many features from that of the present See also:day; mammals appear to have been only poorly represented by puny forms, related to Triassic and Jurassic types; they were mainly marsupials (Batodon, Cimolestes) with a few monotreme-like forms; carnivores, rodents and ungulates were still unknown. As in Jurassic times, See also:reptiles were the dominant forms, and not a few genera lived on from the former period into the Cretaceous; but, on the whole, the reptilian assemblage was no longer so varied, and most of the distinctive mesozoic types had passed away before the close of this period. Dinosaurs were represented by herbivorous and carnivorous genera as in the Jurassic period, but the latter were less abundant than before. The See also:Iguanodon of the See also:Sussex-Weald and Bernissart in Belgium is perhaps the best-known genus; but there were many others, their remains being particularly abundant and well-preserved in the Cretaceous deposits of N. America. Titanosaurus, Acanthopholis, Megalosaurus and Hypsilophodon may be mentioned, some of these being of great See also:size, while Diclonius was a curious See also:duck-billed creature; but most remarkable in appearance must have been the horned Dinosaurs, Ceratops and Triceratops, See also:gross, unwieldy creatures, 25 to 30 ft. See also:long, whose huge heads were grotesquely armed with horns and bony frills. Coincident, perhaps, with the widespread extension of the sea was the development of aquatic habits and structuressuitable thereto amongst all the reptilian See also:groups including also the birds. The foremost place was undoubtedly taken by the pythonomorphs or sea-serpents, including M osasaurus and many others; these were enormously elongated creatures, reaching up to 75 ft., with See also:swimming flappers and powerful swimming tails, and they lived a predatory life in the open sea. Ichthyosaurians soon disappeared from Cretaceous waters; but the plesiosaurians (Cimoliosaurus and others) reached their maximum development in this period. The remarkable flying lizards, pterosaurs, likewise attained their great development and then passed away; they ranged in size from that of a See also:pigeon to creatures with a wing-spread of 25 ft.; notable genera are Pteranodon, Ornitho-cheirus, Nyctiosaurus. See also:Ordinary See also:lizard-like forms were represented by Coniosaurus, Dolichosaurus, &c.; and true crocodiles, Goniopholis, Suchosaurus, appeared in this period, and continued to approximate to modern genera. The earliest known river turtles are found in the Belly River deposits of Canada; marine turtles also made their first appearance and were widely represented, some of them, Archelon and Protostega, being of great size. True See also:snakes appeared later in the period. The birds, as far as existing evidence goes, were aquatic; some, like Ichthyornis, were built for powerful See also:flight; others, like Hesperornis, were flightless. Enaliornis is a form well known from the Cambridge Greensand. They were toothed birds having structural See also:affinities with the Dinosaurs and See also:Pterodactyles. See also:Fish remains of this period show that a marked See also:change was taking place; teleosteans (with bony See also:internal See also:skeleton) were taking a more prominent place, and although ganoids were still represented (Macropoma, Lepidotus, Amiopris, &c.) they had quite ceased to be the dominant types before the close of Cretaceous times. Sharks and rays were of the modern types, though distinct in species. Amongst the early forms of Cretaceous teleosteans may be mentioned Elopopsis, Ichthyodectes, Diplomystus (See also:herring), Haplopteryx and Urenchelys (See also:eel). For further information see the articles CHALK; GREENSAND; WEALDEN. See also:Sir A. See also:Geikie's See also:Text-See also:book of Geology, vol. ii. (4th ed., 1903), contains in addition to a full general See also:account of the system very full references to the literature. Additional information and CommentsThere are no comments yet for this article.
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