Showing papers on "Gondwana published in 1990"

Revised World maps and introduction

Abstract: We review the highlights of the 1988 symposium on Palaeozoic Biogeography and Palaeogeography, and present a revised set of 20 Palaeozoic base maps that incorporate much of the new data presented at the symposium. The maps include 5 major innovations: (1) A preliminary attempt has been made to describe the motion of the Cathaysian terranes during the Palaeozoic; (2) a more detailed description of the events surrounding the Iapetus Ocean is presented; (3) an alternative apparent polar wandering path for Gondwana has been constructed using the changing distributions of palaeoclimatically restricted lithofacies; (4) new palaeomagnetic data have been incorporated that places Laurentia and Baltica at more southerly latitudes, and adjacent to Gondwana, during the Early Devonian; Siberia is also placed further south in the light of biogeographic data presented at the symposium; (5) Kazakhstan is treated as a westward extension of Siberia, rather than as a separate palaeocontinent. The relationships between climatic changes, sea level changes, evolutionary radiations and intercontinental migrations are discussed

Geodynamic Evolution of the Iberian Massif

Abstract: The Iberian Massif represents the largest continuous exposure of pre-Permian rocks within the Iberian Peninsula (Fig. 1). It was first described in terms of a coherent tectonic unit by Staub (1926) who considered it to be comprised of Archean basement sequences that had been successively reworked during Caledonian and Herycnian orogenic events. Stille (1924, 1929) contested these ideas and argued, instead, that the Iberian Massif largely records the effects of Hercynian tectonothermal events. This was later documented in more detail by Lotze (1945), who divided the massif into six zones on the basis of contrasting lithologic, structural and/or metamorphic characteristics (Fig. 1). With the advent of plate tectonic concepts, a new view of the Iberian Massif emerged, and many different geodynamic plate models were proposed. Van der Voo (1982) suggested that the Iberian Massif constituted the southwesternmost and largest piece of the so-called Armorican plate, a continental block which appears to have rifted from Gondwana in the early Paleozoic.

Biogeography of Ordovician and Silurian faunas

Abstract: The new reconstructions generated for this volume fit well with the majority of Ordovician and Silurian faunal data and are a great improvement on previous attempts The distribution of selected trilobites, brachiopods and graptolites are plotted on the new maps and confirm the importance of palaeolatitude in controlling the faunal distributions, particularly of the old cratons, which are shown for the Early Ordovician and Late Silurian Two contrasting patterns of cratonic faunas are (a) disjunct or (b) gradational across a large palaeocontinent, eg Gondwana Marginal and deeper-water biofacies show different patterns, which help to define the edges of palaeocontinents, but which are not so constrained in their palaeolatitudinal distributions In contrast pelagic trilobites do not help to define palaeocontinents, but were sensitive to palaeo temperature and palaeolatitude Specific case histories are considered, in particular the closing of Iapetus and the contemporary widening of the Rheic Ocean and the positioning of Avalonia, and the ancestry of the various associated trilobite and brachiopod genera during the later Ordovician The Ashgill deeper-water Foliomena fauna is also plotted

Early-Middle Palaeozoic biogeography of Asian terranes derived from Gondwana

Abstract: Contiguity of the Shan-Thai Terrane and NW Australia is suggested for Cambro-Ordovician times by the close faunal affinities seen in Late Cambrian trilobites, Ordovician molluscs, stromatoporoids, brachiopods and conodonts. Taxa such as Spanodonta and Georgina are found only on these two blocks whilst others have a Shan-Thai North China, Australian distribution. This, with a re-evaluation of early Palaeozoic palaeomagnetism, places Shan-Thai against NW Australia, N China against N Australia, S China against the western Himalayan-Iran region with Indo-China and Tarim lying between S China and Shan-Thai. A palaeomagnetically required anticlockwise rotation of this greater Gondwana from the Early Cambrian to the Middle Ordovician satisfactorily accounts for the changing biogeographic patterns, in particular the differences between North and South China during the Ordovician. Recent studies on micro vertebrates and conodonts suggest that Shan-Thai was still very close to Australia in the Middle Devonian, as seen by similar turiniform thelodont species from western Yunnan, northern Thailand, and South Australia, as well as the polygnathid P. labiosus lineage, species of which have recently been found in Thailand. Continental fish faunas were highly endemic in South China from Silurian through to Early and Middle Devonian, indicating prolonged isolation of this terrane and separation of South China from Gondwana probably in the Silurian. In the Late Devonian, shared biotic assemblages between North China and South China (endemic Zhongning/Wuting plant flora; endemic antiarch placoderm and polybranchiaspid agnathan fishes); and between these Chinese terranes and Australia (sinolepid antiarchs, earlier appearances of certain antiarchs) indicate close continental proximity of these three major regions. New palaeomagnetic data for Ningxia, together with biogeographic data suggests that this region may have constituted a separate 9Hexizoulang Terrane9.

Gondwana's movement over the South Pole during the Palaeozoic: evidence from lithological indicators of climate

Abstract: A statistical technique is described that uses the geographical distribution of lithological indicators of climate (carbonates, evaporites, coals and tillites) to estimate the past position of the geographic pole. This technique was used to estimate the movement of the South Pole across the supercontinent of Gondwana during the Palaeozoic. Our results indicate that during the Cambrian and Early Ordovician the South Pole was located adjacent to northwestern Africa. The pole moved into the Amazon Basin during the Late Ordovician and into south-central Argentina during the Silurian. Throughout the Devonian and Early Carboniferous the pole moved slowly from a location in southern Argentina to a position near the south coast of Africa. From the Late Carboniferous and into the Permian the South Pole swung eastward across central Antarctica. The Early Palaeozoic and Late Palaeozoic portions of the palaeoclimatically determined APW path are in good agreement with available palaeomagnetic data. The Middle Palaeozoic portion of the palaeoclimatically determined APW path agrees better with the palaeomagnetic data that places the South Pole in southern Argentina, than with the palaeomagnetic results that place the Devonian pole in central Africa.

Precambrian tectonic evolution of part of Gondwana, southwestern Australia

Abstract: Southwestern Australia has a long dynamic Precambrian history of crustal fragmentation and aggregation by continental collision and accretion. This interpretation contrasts with the widely held belief that most of Australia was part of a Proterozoic supercontinent in which all tectonic, magmatic, and metamorphic activity was intracontinental. The Pilbara and Yilgarn cratons are two quite different fragments of Archean continental crust that collided to form the Capricorn orogen between 2000 and 1600 Ma. The Albany-Fraser orogen formed along the southern margin of the Yilgarn craton during another major continental collision at 1300 to 1100 Ma. Rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 Ma. Subsequent continental collision along this rifted margin formed the Paterson orogen at 700 to 600 Ma. Therefore, the assembly of this considerable part of Gondwana may not have been completed until about 600 Ma.

Archean and Proterozoic ancestry in late Precambrian to early Paleozoic crustal elements of southern Turkey as revealed by single-zircon dating

Abstract: Detrital zircon ages and paleontology limit the age of the oldest known metasedimentary rocks in the Menderes-Taurus block of southwestern Turkey to between 657 {plus minus}5 Ma and Middle Cambrian (ca. 533 Ma). A mylonitic granite, also part of the basement, yielded a date of intrusion of 543 {plus minus}7 Ma. The scatter of both detrital and xenocryst zircon ages between 612 {plus minus}6 and 3,140 {plus minus}2 Ma virtually precludes northeastern Africa and Arabia as their provenance, but is compatible with a source in the Angara craton of Siberia. These results suggest that the Pan-African evolution in the Middle East may have ended by Angara's collision with Gondwana in the Early Cambrian.

Tectonic History of the Illinois Basin

Abstract: The Illinois basin began as a failed rift that developed during breakup of a supercontinent approximately 550 Ma. A rift basin in the southernmost part of the present Illinois basin subsided rapidly and filled with about 3,000 m of probable Early and Middle Cambrian sediments. By the Late Cambrian, the rift-bounding faults became inactive and a broad relatively slowly subsiding embayment, extending well beyond the rift and open to the Iapetus Ocean, persisted through most of the Paleozoic Era. Widespread deformation swept through the proto-Illinois basin beginning in the latest Mississippian, continuing to the end of the Paleozoic Era. Uplift of basement fault blocks resulted in the formation of many major folds and faults. The timing of deformation and location of these structures in the forelands of the Ouachita and Alleghanian orogenic belts suggest that much of the deformation resulted from continental collision between North America and Gondwana. The associated compressional stress reactivated the ancient rift-bounding faults, upthrusting the northern edge of a crustal block approximately 1,000 m within the rift. Concurrently, dikes (radiometrically dated as Early Permian), sills, and explosion breccias formed in or adjacent to the reactivated rift. Subsequent extensional stress, probably associated with breakup of Pangea, causedmore » the crustal block within the rift to sink back to near its original position. High-angle, northeast- to east-west-trending normal faults, with as much as 1,000 m of displacement, formed in the southern part of the basin. These faults displace some of the northwest trending Early Permian dikes. Structural closure of the southern end of the Illinois basin was caused by uplift of the Pascola arch sometime between the Late Pennsylvanian and Late Cretaceous.« less

Constraints on the locations of Asian microcontinents in Palaeo-Tethys during the Late Palaeozoic

Abstract: Useful constraints for Late Palaeozoic reconstructions of the Palaeo-Tethys and the development of Asia come from tectonic, palaeomagnetic, biogeographic and palaeoclimatic data. Tectonic constraints include the timing of collisions of the microcontinents which traditionally have been regarded as proceeding from north to south, and ranging in time from Late Palaeozoic to the Tertiary. Such a view gives a good account of the palaeobiogeographic connections, but the Mongolo-Okhotsk suture of northern Mongolia continued to close by counterclockwise rotation as late as the Jurassic. The biogeographic provinces are well developed in the Late Palaeozoic due to the relatively steep equator-to-pole gradients, thus as continents rifted from the southern margin of Palaeo-Tethys, they lost their south temperate Gondwanan affinities and acquired sub-tropical to tropical floras and faunas. Eventually, the north temperate Angaran floras and faunas inhabiting the northern margin of Palaeo-Tethys invaded some of the Cathaysian microcontinents by the end of the Palaeozoic. Unfortunately, the tropical Cathaysian floras could have occurred over a considerable latitudinal range (25° N to 25° S) and thus do not provide precise constraints. These floras, however, do contain seed-dispersed plants which implies that most of these separate microcontinents must have been geographically connected while apparently tectonically distinct. The climatically sensitive sediments include tillites and glacio-marine deposits associated with some of the terranes, and with Gondwana, but they are clearly temperate in origin, not polar, and are overlain by carbonates in Gondwana and the terranes. We interpret this as due to a climatic amelioration, rather than to a latitudinal plate motion. Palaeomagnetic data are now available for a number of south Asian microcontinents and enough determinations have now been made in North and South China to show consistency with the tectonic, biogeographic and climatic information. In detail, a southern belt of terranes, from the Helmand block in Iran and Afghanistan, through the Western Qiangtang and Lhasa blocks of Tibet and to the Sibumasu block of Thailand and Malaya, all rifted off the margins of Gondwana in the Permian. Few palaeomagnetic data are available to support this, but the tillites, floras and faunas are shared with the midlatitude portions of Gondwana from Iran, India and Australia. In the Late Permian the Cathaysian flora is known from at least the Helmand and Western Qiangtang blocks, suggesting that they reached lower latitudes, and were in physical contact with other Cathaysian floras, although the nature of this connection is not understood. The major Cathaysian microcontinents of Yangtze, Indochina, Eastern Qiangtang, Sino-Korea and Tarim were tropical throughout the Carboniferous and Permian. Again, a degree of geographic interconnection is implied by their common floras, and this is shared with low latitude portions of Gondwana, including Arabia and North Africa, but the location and nature of the 9land bridges9 are unknown. Collision of Tarim with Asia in the Early Permian and of Sino-Korea with the Mongolian arcs in the Late Permian is indicated from tectonic and biogeographic data, but, as stated above, the Mongolo-Okhotsk suture did not close until the Late Jurassic, thus rotation of the combined Mongolia and Sino-Korean block continued until that time. The other Cathaysian microcentinents collided with Asia about the Late Triassic giving rise to the Indosinian Orogeny.

Provincias magmaticas acidas y evolucion tectonica de Gondwana: Andes chilenos (28-31°S)

Abstract: . The batholiths of the Andean Cordillera in the Atacama and Coquimbo Regions (28-31°S) reflect tectonic processes associated with the evolving margin of the Gondwana supercontinent. The batholiths consist of the Carbonilerous-Lower Permian Elqui Superunit which records the final assembly of Gondwana, and the Permian-Triassic (Lower Jurassic?) Ingaguas Superunit, which coincides with the period of stability of the supercontinent. These events are tied to those occurring along the Gondwana margin from Peru to Australia. The oldest Elqui unit, Guanta, is composed of calc-alkaline tonalites and granodiorites formed along an active continental margin. These granitoids are intruded by leucocratic peraluminous granitoids (Cochiguas and El Volcan units) derived from melting of variable crustal sources. Some of these granitoids have trace element signatures consistent with a high pressure residual mineralogy suggesting that they formed by melting of a thickened crust. All of the Elqui granitoids are mesozonal and show evidence of contemporaneous and post-emplacement deformation. Their uplift is contemporaneous with a compressional deformation (San Rafael Phase) in the Argentine foreland. The Ingaguas Superunit is an association of epizonal, post-collisional, intrusives which include granitoids derived from deep levels in a garnet-bearing thickened crust (Los Carricitos Unit) and hypersilicic, calc-alkaline to transitional A-type granites, indicating extensive crustal melting of a garnet-poor crust. These granites and the synchronous Pastos Blancos Rhyolites are part of the Choiyoi Magmatic Province which extends for more than 2,500 km along the Central and Southern Andes. Regional considerations suggest that the uplift of the Elqui Superunit and the San Rafael Phase could have resulted from the oblique collision of an allochthonous block to the west in the mid-Permian. This collision could explain crustal thickening and the termination of subduction and block rotations in the Argentine Frontal Cordillera. The removal of the inactive subducted plate would favor decompressional melting, generating large volumes of basalt that could accumulate at the base of the crust and produce the crustal melting that formed the Choiyoi Province. A similar Permian collision has also been suggested in the New England Fold 8elt in Australia. These collisions coincide with the end of the rapid movement of Gondwana relative to the South Pole. In the central part of the Gondwana margin from Patagonia to Antarctica, subduction continued until the Jurassic. 'Thermal blanketing' of the mantle by the stationary supercontinent resulted in accumulation of basaltic magmas at the crust-mantle boundary. The basaltic magmas accumulated below the collage of arc magmatic rocks and exotic blocks accreted in the Paleozoie produced extensive melting forming the Gondwana granite-rhyolite provinces. These events preceded the Jurassic dispersal of the Gondwana supercontinent in this region.

Reconstruction of the Laurasian and Gondwanan segments of Permian Pangaea

Abstract: A reappraisal of the geological and geometrical constraints on the fits of the continents around the Atlantic, Indian and circum-Antarctic oceans is used as a base upon which to re-examine Early and Late Permian palaeomagnetic data. The palaeomagnetic poles from each of the three main Late Palaeozoic palaeo-continents: Eurasia, North America, and Gondwana define statistically well determined means for the Early and Late Permian. When these poles are reconstructed, the means, and their associated A 95 cones of confidence do not superimpose. The lack of superposition of Late Palaeozoic palaeomagnetic poles on Wegener-style Pangaea reconstructions based on Mesozoic and younger seafloor spreading geometries has been noted for some time. Most solutions to this problem have involved alternative 9tight fits9 of the Pangaean continents for the Late Palaeozoic. Solutions invoking the non-dipole behaviour of the magnetic field have also been proposed. We examine the geometric consequences of the 9tight fit9 Mesozoic-based Pangaean reconstructions that allow better fit of the palaeomagnetic data and conclude that the magnitudes of overlap (650-950 km) required by these modifications are not compatible with the geological and tectonic evidence from these regions. We prefer to use a 9looser9 Pangaea fit that does not necessarily result in the superposition of palaeomagnetic poles. However, when the individual poles from Europe, North America, and Gondwana are combined into a global mean pole, it is observed that both the 9tight9 and the 9loose9 fit yield virtually indistinguishable mean pole positions. Considering the strong geological and geometrical arguments against the palaeomagnetically derived fits and the lack of a clear statistical difference between the two we use our revised Pangaean reconstruction to determine palaeo-latitudinal framework of the Eurasian, North American, and Gondwanan segments of Pangaea for the Early and Late Permian. The validity of these palaeo-latitudinal reconstructions is tested with climatically sensitive floristic and lithological data by Ziegler, and found to be satisfactory.

Devonian vertebrate distribution patterns and cladistic analysis of palaegeographic hypotheses

Abstract: Early Devonian vertebrate faunal provinces are clearly defined for four regions: Euramerica, Siberia, China, and East Gondwana. The presence of osteostracans in southwest Siberia (Tuva, Minusa Basins) suggests either proximity of the Siberian block to Euramerica, or palaeogeographic separation of the Tuva region. The Knoydart fauna of Nova Scotia demonstrates that the Avalon Terrane was connected to Euramerica by Gedinnian time. Widespread antarctilamnid sharks in Gondwana suggest a distinctive Gondwana vertebrate fauna, isolated by marine barriers from Euramerica in the Early - Middle Devonian. Late Devonian patterns indicate faunal communication between Gondwana and Euramerica by Frasnian time, and between China and East Gondwana in the late Famennian. The Late Devonian base maps require anomalously wide latitudinal distributions for some taxa. Displacement of Turkey along the northern margin of Gondwana provides an intermediate occurrence of phyllolepid placoderms between disjunct distributions in Euramerica and East Gondwana, but the fossil data do not necessarily corroborate geological evidence for displacement. Biogeographic data generally must be interpreted in the context of palaeogeographic hypotheses, and lack of integration with geological and geophysical data sets has been a major problem. Hierarchical analysis using cladistic techniques has the potential for integrating biological, geological, and geophysical data, as illustrated in a cladistic analysis of the Williams and Hatcher model of Appalachian terranes. As an adjunct to map representation, an area cladogram enables a historical sequence of palaeogeographic events to be represented on a single diagram, together with crucial supporting evidence; it presents an analysis rather than synthesis of empirical data, and the hypothesis is more exposed to falsification.

Antarctic paleobiology : its role in the reconstruction of Gondwana

Abstract: Discusses the current status of paleobiology, principally paleobotany and palynology in Antarctica, and the interrelationship of Antarctic floras to those of other Gondwana continents. It provides a broad coverage of the major groups of plants on the one hand, while on the other seeking to evaluate the vegetational history and the physical and biological parameters that influence the distribution of floras through time and space. The biologic activity is discussed within a framework of the geologic history, including the tectonic and paleogeographic history of the region. In addition, it includes will find a comprehensive bibliography of Gondwana paleobotany and palynology.

Paleobiogeographic relationships of angiosperms from the Cretaceous and early Tertiary of the North American area

Abstract: The biogeographic affinities of the Cretaceous and early Tertiary angiosperm floras of the North American area (which includes Meso-America, and the Greater Antilles) have been the subject of considerable interest. Although recent treatments of isolated taxa have shown affinities between North American, European, east Asian and Neotropic floras, the relationships have not been quantified. This study compiles the records of fossils whose familial relationships seem secure. This provides a carefully culled, and uniformly presented review of the Cretaceous and Paleogene record from 1950 to 1989 and supplements LaMotte (1950). A subset of these records, which showed compelling evidence of subfamilial relationships, was analyzed to quantify the relationships of the Cretaceous, Paleocene, Eocene and Oligocene floras to other regions. The analysis suggests that for the entire period 24% of the fossil species had affinities with extant taxa from the Northern Hemisphere; 10% with taxa from the Northern Hemisphere that have a few species in South America; 17% with taxa from Eurasia; 3% with taxa with a disjunct Eurasian-South American pattern; 19% with taxa from South America and/or Africa; 8% with taxa from South America and/or Africa that have an important sister group in southeast Asia; 5% with taxa from the Old World; and 13% with taxa having other distribution patterns. Those fossils with affinities to Laurasian taxa are mostly found in the northern and western portions of the North American area. The fossils with affinities to South American and/or African taxa are found in the southern portions of North America, Meso-America, and the Greater Antilles. The taxa with disjunct distributions show both patterns. These patterns suggest that during this time there were wide-spread temperate elements, found throughout Laurasia; Boreotropical flora elements, distributed in North America, Europe and along the Tethys seaway to southeast Asia; and West Gondwana elements which show dispersion from South America across the proto-Caribbean. The paleobotanical data are compatible with current geological, paleontological and biogeographical studies.

Palaeozoic palaeogeography from palaeomagnetism of the Atlantic-bordering continents

Abstract: Revised palaeogeographic reconstructions of the Atlantic-bordering continents and intervening terranes are presented for the Siluro-Devonian boundary, Early Devonian, and Late Devonian, based on incorporation of new palaeomagnetic results that have become available from Laurentia and Gondwana. The key features of the palaeogeographic model are the transpressive collision between the eastern margin of Laurentia and the northwest South American margin of Gondwana in the Siluro-Devonian, and the subsequent Devonian retreat of the north African margin and the development of a wide ocean between Africa and Europe by the Late Devonian. Although rather complex and involving rapid motions especially of Gondwana, the revised Devonian plate tectonic evolution as indicated by palaeomagnetism is not inconsistent with biogeographic and palaeoclimatological evidence.

Paleozoic and Mesozoic Geological History of Northeastern Africa Based Upon New Interpretation of Nubian Strata (1)

Abstract: The Nubia terrain in southern Egypt and northern Sudan is the type area for strata of mainly Cretaceous age. Because "Nubian Sandstone" or "Nubian Formation" or similar terms were used for strata in other areas and of other stratigraphic positions, the name "Nubian" has become meaningless. This paper summarizes results of field work done in Egypt and Sudan since 1976. Reconstruction of the tectonics and paleogeography of northeast Africa since the early Paleozoic permits division of all strata related broadly to the "Nubian" into three cycles. The Paleozoic cycle (Cambrian to Early Carboniferous) is mainly marine. This cycle was interrupted by the collision of Gondwana with northern continents. The resultant Karoo cycle, representing purely continental sedimentation, exte ded from the Late Cretaceous until the Early Jurassic. The disintegration of Pangea led to a third cycle that began in the Late Jurassic and resulted in the marginal marine to continental strata of the Nubian cycle that ranges in age from Late Jurassic to latest Cretaceous.

Sedimentological evidence for a limited separation between Armorica and Gondwana during the Early Ordovician

Abstract: The vast extent of sedimentation deposits making up the Gres Armoricain and its equivalents over the north Gondwanan domain is used in this study to test the hypothesis of continuity between the Armorica and Gondwana plates during the Early Ordovician. The distribution of continental and marine environments, the large volume of transported elastic material, and the consistent current directions all indicate that the source of sediment supply on the north Gondwanan margin was to the south of the Sahara. Although there were local signs of incipient rifting between the two plates, Armorica was not yet detached from Gondwana by Arenigian time.

The North Karakorum side of the Central Asia geopuzzle

Abstract: An Italian geological team visited a remote and in part never studied area in the northern Hunza region (Pakistan), which represents the link between the Karakorum and Pamir Ranges. The north Karakorum sequence commences in the Permian with terrigenous sediments, followed by shallow- to deep-marine carbonates deposited on a newly formed passive margin. Deep-water sedimentation continued till the end of the Middle Triassic, when carbonate platform conditions resumed. An episode of deltaic red sandstones with orogenic provenance is interbedded in the Liassic, and it is transgressed by a Middle to ?Upper Jurassic shallow water marine unit. Eventually, all of the sequence was faulted and folded, with weak metamorphic imprint, before fluviatile red polygenic conglomerates sealed the succession,in a spectacular unconformity. The north Karakorum provides an example of a microplate that rifted away from Gondwana in the Permian, reached deep-marine conditions in the Early Triassic, and marginally recorded compressive movements in the Liassic. A subsequent orogenic episode points to a reorganization of the southern Asian margin possibly around middle Cretaceous time. Finally, the north Karakorum was affected by strong fold-thrust deformation and low- to very low-grade metamorphism in the Cainozoic, related to the India-Asia collision.

Palaeomagnetic constraints on the position of Gondwana during Ordovician to Devonian times

Abstract: The currently available palaeomagnetic data base for Gondwana is reviewed and using revised rotation parameters for the fit of the southern continents an attempt has been made to construct an apparent polar wander path for Gondwana during Ordovician to Permo-Carboniferous times using a cubic spline fitting technique. Although the density of the data set is still rather sparse and the quality of the data is variable, our approach seems to be justified when tying the apparent polar wander path to selected palaeopoles of high quality. The palaeogeographic scenario based on our results is rather complex. Rapid northward shift of Gondwana during the Ordovician to the Early Silurian and subsequent collision with Laurentia is followed by divergence and the formation of a wide intervening ocean during the Devonian. The final closure of this ocean did not begin before the Late Devonian and was completed by the Late Carboniferous. If the apparent polar wander path presented in this paper is correct, then extremely high drift rates of about 23 cm a -1 have to be postulated for Gondwana during the Late Ordovician-Silurian.

Gondwanan Paleogeography and Paleoclimatology

Abstract: The supercontinent Gondwana would, by its sheer size, be expected to have had a profound influence on climate. In general, the continental interior would be expected to have been dry and temperatures strongly seasonal, especially at times of low sea level. Changes in the position of the continent relative to the South Pole controlled the timing of Southern Hemisphere continental glaciation and, consequently, global sea level.