Carboniferous

The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359.2 Ma (million years ago), to the beginning of the Permian period, about 299.0 Ma (ICS 2004). As with most older geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by 5–10 million years. The Carboniferous is named for the extensive coal beds of that age found in Western Europe. The first third of the Carboniferous is called the Mississippian epoch, and the remainder is called the Pennsylvanian. Conifer trees were introduced in this important and well-known time period.

Subdivisions

The Carboniferous is usually broken into Pennsylvanian (later) and Mississippian (earlier) Epochs. The Faunal stages from youngest to oldest, together with some of their subdivisions, are:

Late Pennsylvanian Gzhelian (most recent)

Noginskian/Virgilian

Late Pennsylvanian Kasimovian

Klazminskian
Dorogomilovksian/Virgilian
Chamovnicheskian/Cantabrian/Missourian
Krevyakinskian/Cantabrian/Missourian

Middle Pennsylvanian Moscovian

Myachkovskian/Bolsovian/Desmoinesian
Podolskian/Desmoinesian
Kashirskian/Atokan
Vereiskian/Bolsovian/Atokan

Early Pennsylvanian Bashkirian/Morrowan

Melekesskian/Duckmantian
Cheremshanskian/Langsettian
Yeadonian
Marsdenian
Kinderscoutian

Late Mississippian Serpukhovian

Alportian
Chokierian/Chesterian/Elvirian
Arnsbergian/Elvirian
Pendleian

Middle Mississippian Visean

Brigantian/St Genevieve/Gasperian/Chesterian
Asbian/Meramecian
Holkerian/Salem
Arundian/Warsaw/Meramecian
Chadian/Keokuk/Osagean/Osage

Early Mississippian Tournaisian (oldest)

Ivorian/Osagean/Osage
Hastarian/Kinderhookian/Chautauquan/Chouteau

Paleogeography

A global drop in sea level at the end of the Devonian reversed early in the Carboniferous; this created the widespread epicontinental seas and carbonate depostion of the Mississippian.(Stanley, 414) There was also a drop in south polar temperatures; southern Gondwanaland was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not.(Stanley, 414) These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost glaciers.(Stanley, 416)

A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard.(Stanley, 414) This sea-level drop and the associated unconformity in North America separates the Mississippian from the Pennsylvanian periods.(Stanley, 414)

The Carboniferous was a time of active mountain-building, as the supercontinent Pangea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America-Europe (Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly-uplifted Appalachians southwestward as the Ouachita Mountains.(Stanley, 414-6) In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although pieces of present east Asia still remained detached.

Rocks and coal

Carboniferous rocks in Europe and eastern North America largely consist of a repeated sequence of limestone, sandstone, shale and coal beds, known as "cyclothems" in the U.S. and "coal measures" in Britain.(Stanley, 426) In North America, the early Carboniferous is largely marine limestone, which accounts for the division of the Carboniferous into two periods in North American schemes. The Carboniferous coal beds provided much of the fuel for power generation during the Industrial Revolution and are still of great economic importance.

The large coal deposits of the Carboniferous primarily owe their existence to two factors. The first of these is the appearance of bark-bearing trees (and in particular the evolution of the bark fiber lignin). The second is the lower sea levels that occurred during the Carboniferous as compared to the Devonian period. This allowed for the development of extensive lowland swamps and forests in North America and Europe. Some hypothesize that large quantities of wood were buried during this period because animals and decomposing bacteria had not yet evolved that could effectively digest the new lignin. The extensive burial of organically-produced carbon led to a buildup of surplus oxygen in the atmosphere; estimates place the peak oxygen content as high as 35%, compared to 21% today.^* This oxygen level probably increased wildfire activity, as well as resulted in insect and amphibian gigantism--creatures whose size is constrained by respiratory systems that are limited in their ability to diffuse oxygen.

In eastern North America, marine beds are more common in the older part of the period than the later part and are almost entirely absent by the late Carboniferous. More diverse geology existed elsewhere, of course. Marine life is especially rich in crinoids and other echinoderms. Brachiopods were abundant. Trilobites became quite uncommon. On land, large and diverse plant populations existed. Land vertebrates included large amphibians.

Life

Marine Invertebrates

In the oceans the most important groups are the foraminifera, corals, bryozoa, brachiopods, ammonoids, echinoderms (especially crinoids), and Chondrichthyes (sharks and their relatives).

For the first time foraminifera take a prominent part in the marine faunas. The large spindle-shaped genus Fusulina and its relatives were abundant in what is now Russia, China, Japan, North America; other important genera include Valvulina, Endothyra, Archaediscus, and Saccammina (the latter common in Britain and Belgium). Some Carboniferous genera are still extant.

The microscopic shells of Radiolaria are found in cherts of this age in the Culm of Devonshire and Cornwall, and in Russia, Germany and elsewhere.

Sponges are known from spicules and anchor ropes, and include various forms such as the Calcispongea Cotyliscus and Girtycoelia, and the unusual colonial glass sponge Titusvillia.

Both reef-building and solitary corals diversify and flourish; these include both rugose (e.g. Canina, Corwenia, Neozaphrentis), heterocorals, and tabulate (e.g. Chaetetes, Chladochonus, Michelinia) forms.

Conularids were well represented by Conularia

Bryozoa are abundant in some regions; the Fenestellids including Fenestella, Polypora, and the remarkable Archimedes, so named because it is in the shape of an Archimedean screw.

Brachiopods are also abundant; they include Productids, some of which (e.g. Gigantoproductus) reached very large (for brachiopods) size and had very thick shells, while others like Chonetes were more conservative in form. Athyridids, Spiriferids, Rhynchonellids, are Terebratulids are also very common. Inarticulate forms include Discina and Crania. Some species and genera had a very wide distribution with only minor variations.

Annelids such as Spirorbis and Serpulites are common fossils in some horizons.

Among the mollusca, the bivalves continue to increase in numbers and importance. Typical genera include Aviculopecten, Posidonomya, Nucula, Carbonicola, Edmondia, and Modiola

Conocardium is a common Rostoconch.

Gastropods are also numerous, including the genera Murchisonia, Euomphalus, Naticopsis.

Nautiloid cephalopods are represented by tightly coiled nautilids, with straight-shelled and curved-shelled forms becoming increasingly rare. Goniatite Ammonoids are common.

Trilobites are rare, represented only by the proetid group. Ostracods such as Cythere, Kirkbya, and Beyrichia are abundant.

Amongst the echinoderms, the crinoids were the most numerous. Dense submarine thickets of long-stemmed crinoids appear to have flourished in shallow seas, and their remains were consolidated into thick beds of rock. Prominent genera include Cyathocrinus, Woodocrinus, and Actinocrinus. Echinoids such as Archaeocidaris and Palaeechinus were also present. The Blastoids, which included the Pentreinitidae and Codasteridae and superficially resembled crinoids in the possession of long stalks attached to the sea-bed, attain their maximum development at this time.

Fish

Many fish inhabited the Carboniferous seas; predominantly Elasmobranchs (sharks and their relatives). These included some, like Psammodus, with crushing pavement-like teeth adapted for grinding the shells of brachiopods, crustaceans, and other marine organisms. Other sharks had piercing teeth, such as the Symmoriida; some, the petalodonts, had peculiar cycloid cutting teeth. Most of the sharks were marine, but the Xenacanthida invaded fresh waters of the coal swamps. Among the bony fish, the Palaeonisciformes found in coastal waters also appear to have migrated to rivers. Sarcopterygian fish were also prominent, and one group, the Rhizodonts, reached very large size.

Most species of Carboniferous marine fish have been described largely from teeth, fin spines and dermal ossicles, with smaller freshwater fish preserved whole.

Freshwater fishes were abundant, and include the genera Ctenodus, Uronemus, Acanthodes, Cheirodus, and Gyracanthus.

Plants

Early Carboniferous land plants were very similar to those of the preceding Latest Devonian, but new groups also appeared at this time.

The main Early Carboniferous plants were the Equisetales (Horse-tails), Sphenophyllales (vine-like plants), Lycopodiales (Club mosses), Lepidodendrales (scale trees), Filicales (Ferns), Medullosales (previously included in the "seed ferns", an artificial assemblage of a number of early gymnosperm groups) and the Cordaitales. These continued to dominate throughout the period, but during late Carboniferous, several other groups, Cycadophyta (cycads), the Callistophytales (another group of "seed ferns"), and the Voltziales (related to and sometimes included under the conifers), appeared.

The Carboniferous lycophytes of the order Lepidodendrales, which are cousins (but not ancestors) of the tiny club-moss of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included Lepidodendron (with its fruit cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria. The roots of several of these forms are known as Stigmaria.

The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were epiphytic. Fossil ferns and "seed ferns" include Pecopteris, Cyclopteris, Neuropteris, Alethopteris, and Sphenopteris; Megaphyton and Caulopteris were tree ferns.

The Equisetales included the common giant form Calamites, with a trunk diameter of 30 to 60 cm and a height of up to 20 meters. Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.

Cordaites, a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin-like inflorescence, which bore yew-like berries, is called Cardiocarpus. These plants were thought to live in swamps and mangroves. True coniferous trees (Waichia, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground..

Freshwater and Lagoonal Invertebrates

Freshwater Carboniferous invertebrates include various bivalve molluscs that lived in brackish or fresh water, such as Anthracomya, Naiadiles, and Carbonicola; diverse Crustacea such as Bairdia, Carbonia, Estheria, Acanthocaris, Dithyrocaris, and Anthrapalaemon.

The Eurypterids were also diverse, and are represented by such genera as Eurypterus, Glyptoscorpius, Anthraconectes, Megarachne (originally misinterpreted as a giant spider) amd the specialised very large Hibbertopterus Many of these were amphibious.

Frequently a temporary return of marine conditions resulted in marine or brackish water genera such as Lingula, Orbiculoidea, and Productus being found in the thin beds known as marine bands.

Terrestrial Invertebrates

Fossil remains of air-breathing insects, myriapods and arachnids are known from the late Carboniferous, but so far not from the early Carboniferous. Their diversity when they do appear however show that these arthropods were both well developed and numerous. Among the insect groups are the Syntonopterodea (relatives of present-day mayflies), the abundant and often large sap-sucking Palaeodictyopteroidea, the huge predatory Protodonata (griffinflies), the diverse herbivorous "Protorthoptera", and numerous basal Dictyoptera (ancestors of cockroaches). Many insects have been obtained from the coalfields of Saarbruck and Commentry, and from the hollow trunks of fossil trees in Nova Scotia. Some British coalfields have yielded good specimens: Archaeoptitus, from the Derbyshire coalfield, had a spread of wing extending to more 35 cm; some specimens (Brodia) still exhibit traces of brilliant wing colors. In the Nova Scotian tree trunks land snails (Archaeozonites, Dendropupa) have been found.

Tetrapods

Carboniferous amphibians were diverse and common by the middle of the period, more so than they are today; some were as long as 6 meters, and those fully terrestrial as adults had scaly skin.(Stanley, 411-12) They included a number of basal tetrapod groups classified in early books under the Labyrinthodontia. These had long bodies, a head covered with bony plates and generally weak or undeveloped limbs. The largest were over 2 meters long. They were accompanied by an assemblage of smaller amphibians included under the Lepospondyli, often only about 15 cm long. Some Carboniferous amphibians were aquatic and lived in rivers (Loxomma, Eogyrinus, Proterogyrinus); others may have been semi-aquatic (Ophiderpeton, Amphibamus) or terrestrial (Dendrerpeton, Hyloplesion, Tuditanus, Anthracosaurus).

One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. These included the earliest Sauropsid reptiles (Hylonomus), and the earliest known Synapsida (Archaeothyris). These small lizard-like animals quickly gave rise to many descendants. The amniote egg allowed these ancestors of all later birds, mammals, and reptiles to reproduce on land by preventing the desiccation, or drying-out, of the embryo inside. By the end of the Carboniferous period, the reptiles had already diversified into a number of groups, including protorothyridids, captorhinids, aeroscelids, and several families of pelycosaurs.

References

Dudley, Robert. "Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance." Journal of Experimental Biology 201, 1043-50 (1998) (PDF)

Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.

Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0716728826

External links