1911 Encyclopædia Britannica/Permian
PERMIAN, in geology, the youngest and uppermost system of strata of the Palaeozoic series, situated above the Carboniferous and below the Trias. The term “Permian” (derived from the Russian province of Perm, where the rocks are extensively developed) was introduced in 1841 by Sir R. I. Murchison. In England the series of red sandstones, conglomerates, breccias and marls which overlie the Coal Measures were at one time grouped together in one great formation as the “New Red Sandstone,” in contradistinction to the Old Red Sandstone below the Carboniferous: they were likewise known as the Poikilitic series (from Gr. ποικίλος, mottled) from their mottled or variegated colour. They are now divided into two systems or groups of formations; the lower portion being included in the Palaeozoic series under the name Permian, the upper portion being relegated to the Mesozoic series and termed Trias. In Germany the name Dyas was proposed by J. Marcou for the rocks of this age on account of the twofold nature of the series in Thuringia, Saxony, &c. The intimate stratigraphical relationship that exists in many quarters between the Permian rocks and the Carboniferous beds, and the practical difficulties in the way of drawing a satisfactory base-line to the system, have led to the adoption of the term Perma-carboniferous in South Africa, southern Asia, America, Australia and Russia, for strata upon this horizon: C. W. von Gumbel used “Post-carbon” in this sense. In a similar manner Perma-triassic has been employed in cases where a stratigraphical passage from rocks with Permian fossils to others bearing a Triassic fauna is apparent.
The Permian system in England consists of the following subdivisions:—
|W of England||E of England|
|3. Upper||Red sandstones, clays and gypsum||600 ft.||50-100 ft.|
|2. Middle||Magnesian limestone
|10-30 "||600 "|
|1. Lower||Reddish brown and purple sandstones and marls with calcareous conglomerates and breccias of volcanic rocks||3000 "||100-250 "|
From the thicknesses here given it is evident that the Permian rocks have a very different development on the two sides of England On the east side, from the coast of Northumberland southwards to the plains of the Trent, they consist chiefly of a great central mass of limestone. But on the west side of the Pennine Chain, and extending southwards into the central counties, the calcareous zone disappears, and we have a great accumulation of red, arenaceous and gravelly rocks.
The lower subdivision attains its greatest development in the vale of the Eden, where it consists of brick-red sandstones, the Penrith sandstone series, with some beds of calcareous conglomerate or breccia, locally known as "brockram," derived from the waste of the Carboniferous Limestone. These red rocks extend across the Solway into the valleys of the Nith and Annan, in the south of Scotland, where they lie unconformable on the Lower Silurian rocks. Their breccias consist of fragments of the adjacent Silurian greywackes and shales, but near Dumfries some calcareous breccias or “brockrams” occur. These brecciated masses have evidently accumulated in small lakes or narrow fiords Much farther south, in Staffordshire, and in the districts of the Clent and Abberley Hills, the brecciated conglomerates in the Permian series attain a thickness of 400 ft. They have been shown by Sir A. C. Ramsay to consist in large measure of volcanic rocks, grits, slates and limestones, which can be identified with rocks on the borders of Wales. Some of the stones are 3 ft. in diameter and show distinct striation. The same writer pointed out that these Permian drift-beds cannot be distinguished by any essential character from modern glacial drifts; on the other hand, W. W. King and others have opposed this view. The middle subdivision is the chief repository of fossils in the Permian system. Its strata are not red, but consist of a lower zone of hard brown shale with occasional thin limestone bands (Marl Slate) and an upper thick mass of dolomite (Magnesian Limestone). The latter is the chief feature in the Permian development of the east of England. It corresponds with the Zechstein of Germany, as the Marl Slate does with the Kupfer-schiefer. It is a very variable rock in its lithological characters, being sometimes dull, earthy, fine-grained and fossiliferous, in other places quite crystalline, and composed of globular, reniform, botryoidal, or other irregular concretions of crystalline and frequently internally radiated dolomite. Though the Magnesian Limestone runs as a thick persistent zone down the east of England, it is represented on the Lancashire and Cheshire side by bright red and variegated sandstone covered by a thin group of red marls, with numerous thin courses of limestone, containing Schizodus, Bakevellia and other characteristic fossils of the Magnesian Limestone.
Concerning the rocks classed as Permian in the central counties of England there exists some doubt, for recent work tends to show that the lower parts are clearly related to the Carboniferous rocks by their fossils; while there is little evidence to warrant the exclusion of the higher beds from the Trias. Similarly in south Devon, where red sandstones and coarse breccias are well exposed, it has been found difficult to say whether the series should be regarded as Triassic or Permian, though the prevailing tendency is to retain them in the latter system.
The “Dyas” type of the system is found in enormous masses of strata flanking the Harz Mountains, and also in the Rhine provinces, Saxony, Thuringia, Bavaria and Bohemia. In general terms it may be said that in this region there is a lower sandy and conglomeratic subdivision with an upper one more calcareous; the former is known as the Rothliegende, the latter as the Zechstein group On the south side of the Harz Mountains the following subdivisions are recognized:-
|Zechstein Group.||Upper||Anhydrite, gypsum, rock-salt, dolomite, marl, fetid shale and limestone The amorphous gypsum is thechief member of this group; the limestone is sometimes full of bitumen.|
|Middle||Dolomite (Haupt-dolomit), crystalline granular (Rauchwacke), and fine powdery (Asche) with gypsum at bottom|
|Lower||Zechstein-limestone, an argillaceous, thin-bedded compact limestone 15 to 90 ft. thick.|
|Kupfer schiefer, a black bituminous copper-bearing shale, not more than 2 ft. thick, often much less but very constant|
|Zechstein conglomerate and calcareous sandstone.|
|Rothliegende Group.||Upper||Red sandstones (Kreuznach beds), red shales (Monsig beds) with sheets of melaphyre tuff, and quartz-porphyry-conglomerate (Wadern, Oberhof, Solern and Tambach beds).|
|Lower||Sandstones and glomerates (Tholayer beds) on black shales with poor coal seams and clay ironstones (Lebach and Goldlauter beds)|
|Lower Sandstones and shales with seams of coal on red and grey sandstones and shales with impure limestone; (Cusel beds, including Manebach beds, upper, and Gehren beds, lower)|
The name Rothliegende or Rothtodtliegende (red-dead-layer) was given by the miners because their ores disappeared in the red rocks below the copper-bearing Kupfer-schiefer. The Kupferschiefer, although so thin, has been worked in the Mansfeld district for a long period; it contains abundant remains of fish (Palaeoniscus, Platysomus) and plants (Ullmannia). The beds of rock-salt in the German Zechstein are of the greatest importance; at Sperenberg near Berlin it has been penetrated to a depth of 4000 ft. Associated with the salt, gypsum and anhydrite are numerous potassium and magnesium salts, including carnallite, kieserite and polyhalite, which are exploited at Stassfurt and are the only important potassium deposits known. Permian rocks of the Rothliegende type are scattered over a wide area in France, where the lower beds are usually conformable with the Coal Measures. In the upper beds occur the bituminous or “Boghead” shale of Autun. In Russia strata of this age cover an enormous area, in the Ural region, in the governments of Perm, Kasan, Kostroma, and in Armenia. The Russian Permian shows no sharp division into two series; the two types of deposit tend to be more mixed and include in addition some deposits of the more open sea. The general sequence begins with the Artinsk beds, sandy and marly or conglomeratic beds in closing connexion with the Carboniferous, overlain by the Kungur limestones and dolomites; these are followed by red fresh-water sandstones, over which comes an important series of copper-bearing sandstones and conglomerates. Above this, in Kostroma, Vyatka and Kasan there is a calcareous and dolomitic series, the so-called "Russian Zechstein" with marine fossils; the uppermost beds are red marls, with few fresh-water fossils, the Tartarian beds.
The character of the fossils in the Permian of the Mediterranean and south-east Europe-well exemplified in the deposits of Sicily—together with their more generally calcareous nature, indicate a more open sea and more stable marine conditions than obtained farther north. This sea is traceable across south-east Russia into the middle of Asia, through Turkestan and Persia, into the Salt Range of India, where the Productus limestone may be taken as representative of the normal marine plan of Permian times. Southwards, however, of the Nerbudda River another and quite distinct continental assemblage of deposits holds the ground, viz. the lower portion of the great fresh-water Gondwana system. The coarse Talchir conglomerates at the base are succeeded by the sandstones and shales of the Karharbari group, with numerous coal seams, and these in turn are followed by the Damuda series (upwards of 10,000 ft.) of similar rocks, with ironstones and very valuable coal seams. All these strata are characterized by the presence of the Glossopteris flora. A similar succession of beds has been recorded in north-west Afghanistan. In close relationship with the lower members of the Indian Gondwana series, both as regards fossil contents and lithological characters, are the lower Karoo beds of South Africa (Dwyka conglomerate, Ecca shales and mudstones, Beaufort beds and Kimberley shales), also the coal-bearing beds of the Transvaal; the Permo-carboniferous rocks of Australia (including the rich coal measures of Newcastle, the Greta coal measures and marine beds, upper and lower, of New South Wales; those of Tasmania, the Bowen River beds of Queensland, and the Bacchus Marsh glacial beds of Victoria), and similar rocks in New Zealand (Maitai formation, south island; Dun Mountain limestone and Rimutaka beds of the north island) and South America. In North America Permian rocks occur in the east in Pennsylvania, West Virginia, Maryland and Ohio ("Upper Barren Measures"), and in Prince Edward Island, New Brunswick, where they succeed the Carboniferous rocks very regularly. West of the Mississippi, in Texas (7000 ft, including the Wichita beds, Clear Fork and Double Mountain beds), Kansas and Nebraska, the Permian is more extensive and on the whole is more readily separable from the Carboniferous. Here the lower beds are marine and contain many limestones and dolomite's, the higher beds are mainly red sandstones and marls with gypsum; in Texas it is of interest to note the occurrence of copper-stained strata. These upper "Red Beds" are' often not clearly distinguishable from the Trias.
Life of the Permian Period.—The records of the plants and animals of this period are comparatively meagre. The plants show that a gradual change from the Carboniferous types was in progress. Two floral regions are clearly indicated, a northern and a southern. In the latter, which may be regarded as conterminous with the continent of Gondwana, the Lepidodendrons, Sigillarias, Calamites, &c., of the Coal Measures gave place to a distinct flora, named from the prevalence of Glossopteris, the Glossopteris (tongue-fern) flora. Traces of this southern flora have been found in northern Russia. Gangamopteris, Callipteris, Taeniopteris, Schizopteris, Walchia, Voltzia, Ullmannia, Saportea, Baiera are characteristic Permian genera. Among the larger animals amphibians occupied a prominent position, their footprints being very common in the sandstones; the include numerous Labyrinthodonts, Archegosaurus, Stereorachis, Branchiosaurus. At this time the true reptiles began to leave their remains in the rocks; many highly interesting forms are known—Palaeohatteria, Proterosaurus, Stereosternum; others having certain mammalian characteristics include Pareiosaurus, Cynognathus, Dicynodon. Among the fishes may be mentioned Platysomus, Palaeoniscus, Amblypterus, Pleuracanthus. Turning to the invertebrates, undoubtedly the most interesting feature is gradual introduction into the Cephalopoda of the ammonite-like forms such as Medlicottia, Waagenoceras, Popanoceras, in place of the more simple lobed goniatites of the Carboniferous. Brachiopods (Productus horridus, Bakevellia tumidla), Bryozoa and corals were by no means scarce in the more open Permian seas. Schizodus Schlotheimii, Strophalosia Goldfussi, Myophoria, Leimyalind, Bellerophon are characteristic Permian molluscs. The last of the trilobites appears in the Permian of North America.
The evidence so far obtained indicates that in Permian times much of the land in the northern hemisphere was near the general sea-level, and that conditions of considerable aridity prevailed which involved the repeated isolation and evaporation of marine lagoons and land-locked seas. South of this region in Europe and Asia there extended an open "Mediterranean" sea the "Tethys" of E. Suess; while over an enormous area in the southern hemisphere a great land area was spread, "Gondwana land," the land of the Glossopteris flora. At many points in this vast tract, as we have seen, coarse conglomeratic deposits, Talchir, Dwyka, Bacchus Marsh, &c., indicate profound glacial conditions, which some have thought were present also in Britain, Germany and elsewhere in the north. Moderate earth movements were taking place in North America, where the Appalachian and Ouachita mountains were in course of elevation, and in Europe this was a time of great volcanic activity. In the Saal region volcanic rocks in the lower Rothliegende have been penetrated for 1100 ft without reaching the bottom, and elsewhere in central Europe great sheets of contemporaneous quartz porphyry, granite porphyry, melaphyre and porphyrite are abundant with their corresponding tuffs. Melaphyres and tuffs appear in the Vosges, which in the south of France are enormous masses of melaphyre and quartz porphyry. Basic lavas and tuffs—diabase, pierite, olivine basalt and andesite tuffs—were erupted from many small vents in Ayrshire and the Nith basin, and basic lavas occur also in Devonshire. Volcanic rocks occur also in New Zealand, Sumatra and the Transvaal.
Table of Permian Strata, showing approximate correlations.
|Stages.||Britain||Saxony, Thuringia, Bohemia.||Basin of the Saar.||Alps.||Russia.||India.||North America.|
|Thuringian||Marls and gypsum. Magnesian limestone Marl slate||Salt beds of Strassfurt. Zechstein limestones. Kupfer-schneider.||Zechstein.||Upper red sandstones, breccias and conglomerates||Bellerophon limestone. Dolomites and shales of Neumarkt Sandstones of Groden.||Tartarian Marls. Cephalopod beds of Armenia. Copper-bearing sandstones in Ural region. Limestones and dolomites of Kostroma (Russian Zechstein). Kungur and Artinsk sandstones Beds of Novaya, Zemblya and Spitzbergen.||Talchir beds, Kaharbari group. Damuda group. (?) Panchet group. Productus limestones. Dandote group of Salt range. Productus limestones. Limestone of Chitichan.||Part of Lower Gondwana equivalents in South Africa, Australia and South America||Red beds, Cimarron series.||Kansas Kiger stage.
Salt Fork stage.
|Double Mountain beds of Texas.||Upper Barren Measures of Pennsylvania, Nova Scotia, New Brunswick|
|Punjabian or Saxonian||Red sandstones, conglomerates, breccias and marls doubtfully assigned to this period
Volcanic rocks in Scotland and Devonshire.
|Contemporaneous eruptive rocks||Weissliegendes. Tamach beds. Oberhof beds. Goldlauter beds||Rothliegendes.||Red sandstones with eruptive rocks.
The beds of Kreuznach, Wadern, sotern, Tholey
|Verrucano||Fusuliana limestones||Clear Fork Beds|
|Big Blue series.||Wellington beds.
|Artinskian (marine) or Autunian (continental)||Manebach beds. Brandschiefer beds of Wessig. Gehren beds. Branau beds of Bohemia||Rothliegendes.||Lebach beds. Cusel beds.||Verrucano||Wichita beds|