Carboniferous Period
358.9–298.9 million years ago
|
Mean atmospheric O
2 content over period duration |
ca. 32.5 vol %[1]
(163 % of modern level) |
Mean atmospheric CO
2 content over period duration |
ca. 800 ppm[2]
(3 times pre-industrial level) |
| Mean surface temperature over period duration |
ca. 14 °C[3]
(0 °C above modern level) |
| Sea level (above present day) |
Falling from 120 m to present day level throughout Mississippian, then rising steadily to about 80 m at end of period[4] |
|
The
Carboniferous is a
geologic period and system that extends from the end of the
Devonian Period, at 358.9 ± 0.4 million years ago, to the beginning of the
Permian Period, at 298.9 ± 0.15 Ma. The name
Carboniferous means "coal-bearing" and derives from the Latin words
carbō (“
coal”) and
ferō (“I bear, I carry”), and was coined by geologists
William Conybeare and
William Phillips in 1822.
[5] Based on a study of the British rock succession, it was the first of the modern 'system' names to be employed, and reflects the fact that many
coal beds were formed globally during this time.
[6] The Carboniferous is often treated in North America as two geological periods, the earlier
Mississippian and the later
Pennsylvanian.
[7]
Terrestrial life was well established by the Carboniferous period.
[8] Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into
reptiles, the first fully terrestrial vertebrates.
Arthropods were also very common, and many (such as
Meganeura), were much larger than those of today. Vast swaths of forest covered the land, which would eventually be laid down and become the
coal beds characteristic of the Carboniferous
system. The atmospheric content of oxygen also reached their highest levels in history during the period, 35%
[9] compared with 21% today. This increased the atmospheric density by a third over today’s value.
[9] A minor marine and terrestrial
extinction event occurred in the middle of the period, caused by a change in climate.
[10] The later half of the period experienced
glaciations, low sea level, and
mountain building as the continents collided to form
Pangaea.
Subdivisions
In the United States the Carboniferous is usually broken into
Mississippian (earlier) and
Pennsylvanian (later) subperiods. The Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration.
[11] In Europe the Lower Carboniferous sub-system is known as the
Dinantian, comprising the
Tournaisian and
Visean Series, dated at 362.5-332.9 Ma, and the Upper Carboniferous sub-system is known as the
Silesian, comprising the
Namurian,
Westphalian, and
Stephanian Series, dated at 332.9-290 Ma. The Silesian is roughly contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the
Carboniferous Limestone, the Namurian as the
Millstone Grit, and the Westphalian as the
Coal Measures and
Pennant Sandstone.
The
faunal stages from youngest to oldest, together with some of their subdivisions, are:
Late Pennsylvanian: Gzhelian (most recent)
- Noginskian / Virgilian (part)
Late Pennsylvanian: Kasimovian
- Klazminskian
- Dorogomilovksian / Virgilian (part)
- 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 (part) / Osage (part)
Early Mississippian: Tournaisian (oldest)
- Ivorian / (part) / Osage (part)
- Hastarian / Kinderhookian / 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 deposition of the Mississippian.
[12] 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.
[12] These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost
glaciers.
[12]
A mid-Carboniferous drop in sea level precipitated a major marine extinction, one that hit
crinoids and
ammonites especially hard.
[12] This sea level drop and the associated
unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod.
[12] This happened about 318 million years ago, at the onset of the
Permo-Carboniferous Glaciation.
[citation needed]
The Carboniferous was a time of active
mountain-building, as the
supercontinent Pangaea 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.
[12] 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 North China (which would collide in the Latest Carboniferous), and
South China continents were still separated from
Laurasia. The Late Carboniferous Pangaea was shaped like an "O."
There were two major oceans in the Carboniferous—
Panthalassa and
Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed -
Rheic Ocean (closed by the assembly of
South and
North America), the small, shallow
Ural Ocean (which was closed by the collision of
Baltica and Siberia continents, creating the
Ural Mountains) and
Proto-Tethys Ocean (closed by
North China collision with
Siberia/
Kazakhstania).
Climate and weather
Average global temperatures in the Early Carboniferous Period were high: approximately 20 °C (68 °F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C (54 °F). Glaciations in
Gondwana, triggered by Gondwana's southward movement, continued into the
Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as
Permo-Carboniferous in age.
The thicker atmosphere and stronger
coriolis effect due to Earth's faster rotation (a day lasted for 22.4 hours in early Carboniferous) created significantly stronger winds than today.
[13]
The cooling and drying of the climate led to the
Carboniferous Rainforest Collapse (CRC). Tropical rainforests fragmented and then were eventually devastated by climate change.
[10][14]
Rocks and coal
Carboniferous rocks in Europe and eastern North America largely consist of a repeated sequence of
limestone,
sandstone,
shale and
coal beds.
[15] 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 may owe their existence primarily to two factors. The first of these is the appearance of
wood tissue and
bark-bearing trees. The
evolution of the wood fiber
lignin and the bark-sealing, waxy substance
suberin variously opposed decay organisms so effectively that dead materials accumulated long enough to fossilise on a large scale. The second factor was the lower sea levels that occurred during the Carboniferous as compared to the preceding
Devonian period. This promoted the development of extensive lowland
swamps and
forests in North America and Europe. Based on a genetic analysis of mushroom fungi, David Hibbett and colleagues proposed that large quantities of
wood were buried during this period because animals and decomposing
bacteria had not yet
evolved enzymes that could effectively digest the resistant phenolic lignin polymers and waxy suberin polymers. They suggest that fungi that could break those substances down effectively only became dominant towards the end of the period, making subsequent coal formation much rarer.
[16][17][18]
The Carboniferous trees made extensive use of lignin. They had bark to wood ratios of 8 to 1, and even as high as 20 to 1. This compares to modern values less than 1 to 4. This bark, which must have been used as support as well as protection, probably had 38% to 58% lignin. Lignin is insoluble, too large to pass through cell walls, too heterogeneous for specific enzymes, and toxic, so that few organisms other than
Basidiomycetes fungi can degrade it. To oxidize it requires an atmosphere of greater than 5% oxygen, or compounds such as peroxides. It can linger in soil for thousands of years and its toxic breakdown products inhibit decay of other substances.
[19] Probably the reason for its high percentages is protection from insect herbivory in a world containing very effective insect herbivores, but nothing remotely as effective as modern
insectivores and probably many fewer poisons than currently. In any case coal measures could easily have made thick deposits on well drained soils as well as swamps. The extensive burial of biologically produced
carbon led to an increase in
oxygen levels in the atmosphere; estimates place the peak oxygen content as high as 35%, compared to 21% today.
[20] This oxygen level may have increased
wildfire activity. It also may have promoted
gigantism of
insects and
amphibians — creatures that have been constrained in size by
respiratory systems that are limited in their physiological ability to transport and distribute oxygen at the lower atmospheric concentrations that have since been available.
[21]
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
Plants
Etching depicting some of the most significant plants of the Carboniferous.
Early Carboniferous land plants, some of which were
preserved in
coal balls, were very similar to those of the preceding Late
Devonian, but new groups also appeared at this time.
The main Early Carboniferous plants were the
Equisetales (horse-tails),
Sphenophyllales (scrambling plants),
Lycopodiales (club mosses),
Lepidodendrales (scale trees),
Filicales (ferns),
Medullosales (informally 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 cone called
Lepidostrobus),
Anabathra,
Lepidophloios and
Sigillaria. The roots of several of these forms are known as
Stigmaria. Unlike present day trees, their
secondary growth took place in the
cortex, which also provided stability, instead of the
xylem.
[22] The
Cladoxylopsids were large trees, that were ancestors of ferns, first arising in the Carboniferous.
[23]
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 (24 in) and a height of up to 20 m (66 ft).
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 reproductive organs, which bore ovules/seeds, is called
Cardiocarpus. These plants were thought to live in swamps and mangroves. True coniferous trees (
Walchia, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.
Marine invertebrates
In the oceans the most important
marine invertebrate groups are the
Foraminifera,
corals,
Bryozoa,
Ostracoda,
brachiopods,
ammonoids,
hederelloids,
microconchids and
echinoderms (especially
crinoids). 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
radiolarians are found in
cherts of this age in the
Culm of
Devon 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, the
demosponge Chaetetes, and the genus of unusual colonial
glass sponges Titusvillia.
Both
reef-building and solitary corals diversify and flourish; these include both
rugose (for example,
Caninia,
Corwenia,
Neozaphrentis), heterocorals, and
tabulate (for example,
Chladochonus,
Michelinia) forms.
Conularids were well represented by
Conularia
Bryozoa are abundant in some regions; the fenestellids including
Fenestella,
Polypora, and
Archimedes, so named because it is in the shape of an
Archimedean screw.
Brachiopods are also abundant; they include
productids, some of which (for example,
Gigantoproductus) reached very large (for brachiopods) size and had very thick shells, while others like
Chonetes were more conservative in form.
Athyridids,
spiriferids,
rhynchonellids, and
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
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 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 rarer than in previous periods, on a steady trend towards extinction, represented only by the proetid group.
Ostracoda, a class of
crustaceans, were abundant as representatives of the
meiobenthos; genera included
Amphissites,
Bairdia,
Beyrichiopsis,
Cavellina,
Coryellina,
Cribroconcha,
Hollinella,
Kirkbya,
Knoxiella, and
Libumella.
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 seabed, attain their maximum development at this time.
-
-
Bivalves (Aviculopecten) and brachiopods (Syringothyris) in the Logan Formation (Lower Carboniferous) in Wooster, Ohio.
-
Syringothyris sp.; a spiriferid
brachiopod from the Logan Formation (Lower Carboniferous) of Wooster, Ohio (internal mold).
-
Palaeophycus ichnosp.; a
trace fossil from the Logan Formation (Lower Carboniferous) of Wooster, Ohio.
-
Crinoid calyx from the Lower Carboniferous of Ohio with a conical
platyceratid gastropod (
Palaeocapulus acutirostre) attached.
-
Conulariid from the Lower Carboniferous of Indiana.
-
Tabulate coral (a syringoporid); Boone Limestone (Lower Carboniferous) near Hiwasse, Arkansas.
Freshwater and lagoonal invertebrates
Freshwater Carboniferous invertebrates include various
bivalve molluscs that lived in brackish or fresh water, such as
Anthraconaia,
Naiadites, and
Carbonicola; diverse
crustaceans such as
Candona,
Carbonita,
Darwinula,
Estheria,
Acanthocaris,
Dithyrocaris, and
Anthrapalaemon.
The upper Carboniferous giant spider-like eurypterid
Megarachne grew to legspans of 50 cm (20 in).
The
Eurypterids were also diverse, and are represented by such genera as
Anthraconectes,
Megarachne (originally misinterpreted as a giant spider) and 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,
[24] myriapods and
arachnids[25] are known from the late Carboniferous, but so far not from the early Carboniferous.
[8] The first true
priapulids appeared during this period. Their diversity when they do appear, however, shows that these arthropods were both well developed and numerous. Their large size can be attributed to the moistness of the environment (mostly swampy fern forests) and the fact that the oxygen concentration in the Earth's atmosphere in the Carboniferous was much higher than today.
[26] This required less effort for respiration and allowed
arthropods to grow larger with the up to 2.6 metres long millipede-like
Arthropleura being the largest known land invertebrate of all time. Among the insect groups are the huge predatory
Protodonata (griffinflies), among which was
Meganeura, a giant
dragonfly-like insect and with a wingspan of ca. 75 cm (30 in) — the largest flying insect ever to roam the planet. Further groups are the
Syntonopterodea (relatives of present-day
mayflies), the abundant and often large sap-sucking
Palaeodictyopteroidea, the diverse herbivorous
Protorthoptera, and numerous
basal Dictyoptera (ancestors of
cockroaches).
[24] Many insects have been obtained from the coalfields of
Saarbrücken 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 than 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.
-
The late Carboniferous giant dragonfly-like insect
Meganeura grew to wingspans of 75 cm (30 in).
-
The gigantic
Pulmonoscorpius from the early Carboniferous reached a length of up to 70 cm (28 in).
-
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 fish were abundant, and include the genera
Ctenodus,
Uronemus,
Acanthodes,
Cheirodus, and
Gyracanthus.
Sharks (especially the
Stethacanthids) underwent a major
evolutionary radiation during the Carboniferous.
[27] It is believed that this evolutionary radiation occurred because the decline of the
placoderms at the end of the Devonian period caused many
environmental niches to become unoccupied and allowed new organisms to evolve and fill these niches.
[27] As a result of the evolutionary radiation carboniferous sharks assumed a wide variety of bizarre shapes including
Stethacanthus which possessed a flat brush-like dorsal fin with a patch of
denticles on its top.
[27] Stethacanthus' unusual fin may have been used in mating rituals.
[27]
-
-
Falcatus was a Carboniferous shark, with a high degree of sexual dimorphism.
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.
[28] 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 (6 in) long. Some Carboniferous amphibians were aquatic and lived in rivers (
Loxomma,
Eogyrinus,
Proterogyrinus); others may have been semi-aquatic (
Ophiderpeton,
Amphibamus,
Hyloplesion) or terrestrial (
Dendrerpeton,
Tuditanus,
Anthracosaurus).
The
Carboniferous Rainforest Collapse slowed the evolution of amphibians who could not survive as well in the cooler, drier conditions. Reptiles, however prospered due to specific key adaptations.
[10] 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
synapsid (
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.
Reptiles underwent a major evolutionary radiation in response to the drier climate that preceded the rainforest collapse.
[10][29] By the end of the Carboniferous period,
amniotes had already diversified into a number of groups, including
protorothyridids,
captorhinids,
araeoscelids, and several
families of
pelycosaurs.
Fungi
Because plants and animals were growing in size and abundance in this time (for example,
Lepidodendron), land
fungi diversified further. Marine fungi still occupied the oceans. All modern
classes of fungi were present in the Late Carboniferous (
Pennsylvanian Epoch).
[30]
Extinction events
Romer's gap
The first 15 million years of the Carboniferous had very limited terrestrial fossils. This gap in the fossil record is called
Romer's gap after the American palaentologist
Alfred Romer. While it has long been debated whether the gap is a result of fossilisation or relates to an actual event, recent work indicates the gap period saw a drop in atmospheric oxygen levels, indicating some sort of ecological collapse.
[31] The gap saw the demise of the
Devonian fish-like
ichthyostegalian labyrinthodonts, and the rise of the more advanced
temnospondyl and
reptiliomorphan amphibians that so typify the Carboniferous terrestrial vertebrate fauna.
Carboniferous rainforest collapse
Before the end of the Carboniferous Period, an
extinction event occurred. On land this event is referred to as the
Carboniferous Rainforest Collapse (CRC).
[10] Vast tropical rainforests collapsed suddenly as the
climate changed from hot and humid to cool and arid. This was likely caused by intense
glaciation and a drop in sea levels.
[32]
The new climatic conditions were not favorable to the growth of rainforest and the animals within them. Rainforests shrank into isolated islands, surrounded by seasonally dry habitats. Towering
lycopsid forests with a heterogeneous mixture of vegetation were replaced by much less diverse tree-fern dominated flora.
Amphibians, the dominant vertebrates at the time, fared poorly through this event with large losses in biodiversity; reptiles continued to diversify due to key adaptations that let them survive in the drier habitat, specifically the hard-shelled egg and scales, both of which retain water better than their amphibian counterparts.
[10]
