Southern Hemisphere Continents Research Articles

Climate change: a cause for new biodiversity conservation objectives but let’s not throw the baby out with the bathwater

Climate change: a cause for new biodiversity conservation objectives but let’s not throw the baby out with the bathwater

A re-evaluation of the ‘mid-Cretaceous sauropod hiatus’ and the impact of uneven sampling of the fossil record on patterns of regional dinosaur extinction

The mid-Cretaceous of North America and Europe has long been noted for the absence of sauropod dinosaurs, leading several authors to suggest that this depauperate interval is a consequence of an end-Albian sauropod extinction. This time period has become known as the ‘mid-Cretaceous sauropod hiatus’, with the subsequent presence of titanosaurian sauropods in the latest Cretaceous of North America and Europe interpreted as the result of dispersal of taxa from South America and Africa, respectively. However, several lines of evidence indicate that this hiatus is probably a sampling artefact. New fossil and trackway discoveries have considerably shortened the hiatus, reducing it to the Turonian–early Campanian in North America, and to just two short intervals in the late Cenomanian–early Turonian and late Coniacian–Santonian of Europe. Palaeoenvironmental analyses of sauropods demonstrate an inland terrestrial preference for titanosaurs, the dominant Late Cretaceous sauropods; however, during the hiatus there was a decline in inland deposits and increase in coastal sediments in Europe and North America, which would have greatly reduced the probability of preserving titanosaurs. Neither the decline in inland deposits, nor the ‘sauropod hiatus’, occurred elsewhere in the world. Statistical comparisons also demonstrate a significant positive correlation between fluctuations in inland deposits and sauropod occurrences during the mid–Late Cretaceous in Europe and North and South America. Lastly, cladistic analyses do not place latest Cretaceous North American and European titanosaurs within South American and African clades, contradicting the predictions of the ‘austral immigrant’ hypothesis. The latter hypothesis also receives little support from biogeographical analysis of dispersal among titanosaurs. Thus, the ‘sauropod hiatus’ of North America and Europe is most plausibly interpreted as the product of a sampling bias pertaining to the rarity of inland sediments and dominance of coastal deposits preserved in these two regions during the mid-Cretaceous. The presence of titanosaurs in these areas during the latest Cretaceous can be explained by dispersal from Southern Hemisphere continents, but this is no more probable than descent from Early Cretaceous incumbent faunas or dispersal from Asia.

Climatic patterns in equatorial and southern Africa from 30,000 to 10,000 years ago reconstructed from terrestrial and near-shore proxy data

As part of a wider study of last glacial and deglacial climates in the Southern Hemisphere continents, we here review terrestrial and near-shore marine records from equatorial and southern Africa between 30,000 and 10,000 years ago (30–10 ka). This time interval covers the lead-up to the Last Glacial Maximum (LGM; 21 ± 2 ka), the LGM proper, and the ensuing deglacial. Records selected for review needed to meet three requirements: continuity or near continuity over the period; a well-established chronology; and at least one but preferably several unambiguous proxy(ies). We aim to show how regional climates of the sub-continent have responded to orbital forcing as opposed to other global glacial-interglacial boundary conditions, and how they are related to high latitude climates, sea and land surface conditions, positions of the Intertropical Convergence Zone (ITCZ) and of the westerly belt. Evidence of past climates derived from many independent proxies is given from west to southwest Africa (moisture from the Atlantic Ocean), then from equatorial East Africa to the southern subtropical summer rainfall domain (moisture mainly from the Indian Ocean). The LGM was cooler than today, and generally drier in the tropics. North of 8–9°S, glacial to Holocene increase in monsoonal precipitation, primarily related to orbitally-induced summer insolation in the northern hemisphere, occurred by steps of increasing amplitude (∼17–16, 14.5, 11.5 ka). Major wet–dry spells coincide with abrupt warm–cold events in high northern latitudes and related ITCZ migrations. In the southern tropics, the main post-glacial increase in tropical rainfall generally appears more gradual and in phase with Antarctic warming. Data suggest a restricted northward migration of the ITCZ and concentration of tropical rainfall well south of the Equator during the LGM and the Younger Dryas. Drier glacial conditions prevailed in southeastern Africa, while parts of southwestern Africa point to enhanced humidity during the LGM, suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive Antarctic sea-ice. Inferred African climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres, and suggest changes in both meridional and zonal circulation modes. This review also reveals major geographical and methodological gaps, and a number of unresolved issues providing pointers for future research.

Bees

Bees

Redescription of the Antarctic springtail Desoria klovstadi using morphological and molecular evidence

Isotoma klovstadi Carpenter, 1902 was one of the first Collembola described from the Antarctic continent. It was first collected in November 1899 during the British Antarctic Expedition on the north coast of Victoria Land in the Ross Sea region. It is now known to occur in an extensive area of northern Victoria Land, including the offshore Possession, Coulman, and Foyn Islands. More recently, L klovstadi was moved to the genus Gnathisotoma Cassagnau, 1957 and has been included in this genus in an unpublished checklist (online) of all described Collembola. Here, we redescribe the species and use morphological and molecular (COI and 18S genes) evidence to investigate its affinities within the Isotominae. We show that it does not belong to Gnathisotoma, or Isotoma s. str. (the viridis group) as currently conceived, but is likely to be part of the species complex of Isotoma s. lat. We discuss reasons for placing it in the genus Desoria Nicolet, 1841. Our results reinforce the already high level of endemicity in the Antarctic fauna and emphasise the value of both morphological and molecular studies in examining relict Gondwanan taxa and their evolutionary relationships with those of other Southern Hemisphere continents. (Less)

The biogeography of the austral, subalpine genus Ourisia (Plantaginaceae) based on molecular phylogenetic evidence: South American origin and dispersal to New Zealand and Tasmania

Molecular phylogenetic analyses of 26 of the 28 species of Ourisia, including eight of ten subspecies and two purported natural hybrids, are presented and used to examine the biogeography of the genus, which is distributed in subalpine to alpine habitats of South America, New Zealand and Tasmania. Gondwanan vicariance, often cited as the cause of this classic austral biogeographical pattern, was rejected by parametric bootstrapping of our combined dataset. Alternatively, various lines of evidence are presented in favour of a South American origin of Ourisia and subsequent dispersal to Australasia. Specifically, the genus likely arose in the Andes of central Chile and spread to southern Chile and Argentina, to the north-central Andes, and finally to Tasmania and New Zealand. The ancestor of the New Zealand species probably first arrived on the South Island, where the New Zealand species of Ourisia are most diverse, and migrated to the North and Stewart Islands. Because the Tasmanian and New Zealand species are sister to one another, the direction of dispersal between these two areas is equivocal. These results agree with other molecular phylogenetic studies that show that past dispersal between southern hemisphere continents has played an important role in the evolutionary history of many high-elevation austral plants. Our data also show that within South America, many of the geographical barriers (with the exception of the Atacama Desert) that have played a role in the evolution of other plant groups have not affected Ourisia species. Within New Zealand, the phylogeny and biogeography of species of Ourisia coincide with the geological history of the country and patterns of other alpine plants. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 479–513.

Ice core evidence for secular variability and 200-year dipolar oscillations in atmospheric circulation over East Antarctica during the Holocene

Two Holocene ice core records from East Antarctica (Vostok and EPICA-Dome C) were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per ~50 years. A series of volcanic markers randomly distributed over the common part of the ice cores (from 9.8 to 3.5 kyear BP) ensures accurate relative dating (±33 years). Dust-size records from the two sites display oscillations structured in cycles with sub-millennial and secular scale frequencies that are apparently asynchronous. The power spectra of the composite sum (Σ) of the two dust-size records display spectral energy mostly for 150- to 500-year periodicities. On the other hand, the 200-year band is common to both records and the 200 year components of the two sites are out-of-phase (100-year lead or lag) over ~5.5 kyear, a phenomenon also reflected by a significant (>99% conf. lev.) band in the power spectra of the composite difference (Δ) of the two size records. During long-range transport, mineral dust originating from the Southern Hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport. Relatively coarse dust is associated with air mass penetration from the middle–lower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the Antarctic plateau, a hypothesis already proposed for the changes that occurred during the Last Glacial Maximum to Holocene transition (Delmonte et al. 2004b). Moreover, we assume that the overall fluctuation of air mass advection over Antarctica depends on the meridional pressure gradient with respect to low latitudes, i.e. the Antarctic Oscillation (AAO). We therefore suggest a regional variability in atmospheric circulation over East Antarctica. The 150–500 year power spectrum of the composite (Σ) parameter represents the long term variability of the AAO, imprinted by secular internal oscillations probably related to the southern ocean-climatic system. On the other hand, the Δ dust composite parameter suggests a persistent atmospheric dipole over East Antarctica delivering coarser (finer) dust particles alternatively to Vostok and Dome C regions with a bi-centennial periodicity. Indeed, a seesaw phenomenon in dust size distribution was already observed at three East Antarctic sites during the last deglaciation (Delmonte et al. 2004b) and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole. Interestingly, the Δ parameter shows a pronounced 200-year oscillation mode, throwing new light on the unresolved question of a possible relationship between climate and solar activity.

The phylogenetic history and biogeography of the frankincense and myrrh family (Burseraceae) based on nuclear and chloroplast sequence data

Generalized hypotheses for the vicariant, Gondwanan origin of pantropically distributed eudicotyledon families must be refined to accommodate recently revised dates that indicate major continental rifting events predate the evolution of many tricolpate angiosperm clades. Here, we use molecular phylogenies of an eudicotyledon family previously hypothesized to have a Gondwanan origin, the Burseraceae, to test this and other alternative biogeographical hypotheses in light of recalibrated geological events. Phylogenies based on nuclear and chloroplast data were reconstructed for 13 of the 18 genera (50 spp. total) of Burseraceae using parsimony, maximum likelihood, and Bayesian methods. Ages of all lineages were estimated using penalized likelihood and semiparametric rate smoothing [Bioinformatics 2003 (19) 301], which allows the user to calibrate phylogenies based on non-clock-like DNA sequence data with fossil information. Biogeographical hypotheses were tested by comparing ages of species and more inclusive lineages with their extant and most parsimonious ancestral distributions. Our data support a North American Paleocene origin for the Burseraceae followed by dispersal of ancestral lineages to eastern Laurasia and Southern Hemisphere continents.

Variability in Terrestrial Carbon Sinks over Two Decades. Part III: South America, Africa, and Asia

Abstract Seventeen years (1982–98) of net carbon flux predictions for Southern Hemisphere continents have been analyzed, based on a simulation model using satellite observations of monthly vegetation cover. The NASA Carnegie Ames Stanford Approach (CASA) model was driven by vegetation-cover properties derived from the Advanced Very High Resolution Radiometer and radiative transfer algorithms that were developed for the Moderate Resolution Imaging Spectroradiometer (MODIS). The terrestrial ecosystem flux for atmospheric CO2 for the Amazon region of South America has been predicted between a biosphere source of –0.17 Pg C per year (in 1983) and a biosphere sink of +0.64 Pg C per year (in 1989). The areas of highest variability in net ecosystem production (NEP) fluxes across all of South America were detected in the south-central rain forest areas of the Amazon basin and in southeastern Brazil. Similar levels of variability were recorded across central forested portions of Africa and in the southern horn of East Africa, throughout Indonesia, and in eastern Australia. It is hypothesized that periodic droughts and wildfires associated with four major El Niño events during the 1980s and 1990s have held the net ecosystem carbon sink for atmospheric CO2 in an oscillating pattern of a 4–6-yr cycle, despite observations of increasing net plant carbon fixation over the entire 17-yr time period.

Soil Functional Responses to Excess Nitrogen Inputs at Global Scale

There is little evidence that nitrogen (N) cycling in the highly weathered, low-phosphorus (P), acidic soils found in Southern Hemisphere continents will differ greatly from that in North America and Europe. Evidence from the 'south' shows: the similarity in forms and temporal patterns in losses of N from different land uses; that the C:N ratios of the forest floor/litter layer from different continents are strongly predictive of a range of processes on a global scale; that generalizations based on Northern Hemisphere experience of the impact of N additions to 'P-limited' ecosystems are likely to fail for southern ecosystems where anatomical and physiological adaptation of native plants to low-P soils makes questionable the concept of 'P-limitation'; that the greatest threats in the 'south' are probably changes in land use that may greatly increase N inputs and turnover; that localized increases in N inputs produce similar effects to those seen in the 'north'.

First Characterization and Dating of East Antarctic Bedrock Inclusions from Subglacial Lake Vostok Accreted Ice

Environmental Context.Lake Vostok is a large subglacial lake trapped below the East Antarctic ice sheet. The meteoric ice from deep Vostok ice cores has been used to document the climatic history of the Earth over hundreds of millennia, while the deeper part of the core preserves some basal rock fragments. These rock fragments represent unique geological samples of the inhospitable, ice-covered East Antarctic Plateau. Abstract.The Vostok (East Antarctica, 78°S, 106°E) ice core preserves, below the meteoric ice keeping the climatic memory of the last 420 000 years, ice formed by freezing of subglacial Lake Vostok water. This latter contains some bedrock fragments representing unique samples for the geological investigation of the East Antarctic Plateau, covered by ~2–4 km of ice. The first geochemical (87Sr/86Sr versus 143Nd/144Nd) and mineralogical characterization of these inclusions as well as the dating of one of them (Nd model age on whole-rock sample) has given evidence for a Mid-Proterozoic age of the basement lying below the ice sheet, consistent with recent geophysical data. The geochemical characteristics of bedrock inclusions within the accreted ice zone are markedly different from those of the mineral dust of aeolian origin archived in the uppermost part of the Vostok ice core and originating from deflation of the Southern Hemisphere continents, and easily discriminates between the two contributions.

Refining the isotopic (Sr-Nd) signature of potential source areas for glacial dust in East Antarctica

The geographical origin of the mineral dust transported to the East Antarctic Plateau from the Southern Hemisphere (SH) continents has been investigated by means of the isotopic (Sr-Nd) signature of samples from Potential Source Areas (PSAs). Dust reaching Antarctica is fine-grained (<5 um), and therefore the new isotopic fields have been defined in the equivalent size range. The so obtained dataset evidences a partial overlap among the signatures of the Ice Core dust and South America, New Zealand and the Antarctic Dry Valleys, while South Africa appear distinctly different; further data are needed for the Australian continent. Despite the geochemical similarity with the Dry Valleys and New Zealand, Southern South America still appears to be the most probable source for dust in Antarctica in glacial times.

The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism

The concept of ‘Gondwana’, an ancient Southern Hemisphere supercontinent, is firmly established in geological and biogeographical models of Earth history. The term Gondwana (Gondwanaland of some authors) derives from the recognition by workers at the Indian Geological Survey in the mid- to late 19th century of a distinctive sedimentary sequence preserved in east central India. This succession, now known to range in age from Permian to Cretaceous, is lithologically and palaeontologically similar to coeval non-marine sedimentary successions developed in most of the Southern Hemisphere continents suggesting former continuity of these landmasses. Palaeomagnetic data and tectonic reconstructions suggest that the main assembly of Gondwana took place around the beginning of the Palaeozoic in near-equatorial latitudes and that the supercontinent as a whole shifted into high southern latitudes, allowing widespread glaciation by the end of the Carboniferous. From Carboniferous to Cretaceous times the southern continents had broadly similar floras but some species-level provincialism is apparent at all times. The break-up of Gondwana initiated during the Jurassic (at about 180 million years ago) and this process is continuing. The earliest rifting (crustal attenuation) within the supercontinent initiated in the west (between South America and Africa) and in general terms the rifting pattern propagated eastward with major phases of continental fragmentation in the Early Cretaceous and Late Cretaceous to Paleogene. Gondwanan floras show radical turnovers near the end of the Carboniferous, end of the Permian and the end of the Triassic that appear to be unrelated to isolation or fragmentation of the supercontinent. Throughout the late Palaeozoic and Mesozoic the high-latitude southern floras maintained a distinctly different composition to the palaeoequatorial and boreal regions even though they remained in physical connection with Laurasia for much of this time. Gondwanan floras of the Jurassic and Early Cretaceous (times immediately preceding and during break-up) were dominated by araucarian and podocarp conifers and a range of enigmatic seed-fern groups. Angiosperms became established in the region as early as the Aptian (before the final break-up events) and steadily diversified during the Cretaceous, apparently at the expense of many seed-fern groups. Hypotheses invoking vicariance or long distance dispersal to account for the biogeographic patterns evident in the floras of Southern Hemisphere continents all rely on a firm understanding of the timing and sequence of Gondwanan continental breakup. This paper aims to summarise the current understanding of the geochronological framework of Gondwanan breakup against which these biogeographic models may be tested. Most phytogeographic studies deal with the extant, angiosperm-dominated floras of these landmasses. This paper also presents an overview of pre-Cenozoic, gymnosperm-dominated, floristic provincialism in Gondwana. It documents the broad succession of pre-angiosperm floras, highlights the distinctive elements of the Early Cretaceous Gondwanan floras immediately preceding the appearance of angiosperms and suggests that latitudinal controls strongly influenced the composition of Gondwanan floras through time even in the absence of marine barriers between Gondwana and the northern continents.

Palaeomagnetism and the reconstruction of gondwanaland

The past existence of the supercontinent Gondwanaland has been regarded as the basis of a now respectable hypothesis which explains the present distribution of rock types peculiar to the southern hemisphere continents and India. Gondwana geologists were clearly attracted to the hypothesis even though specific details of the reconstruction remained unresolved. Much credence has been given to reconstructions based on computer matching of continental-shelf morphologies: the palaeomagnetic data provided insufficient resolution to be used exclusively for detailed intercontinental reconstructions. The geometrical fit of South America to Africa and Australia to Antarctica left little to question whereas the relationship of western Gondwanaland (Africa and South America) to eastern Gondwanaland (Australia, Antarctica and India) has long been a topic for discussion. The detail of that fit depended primarily on the pre-drift position of Madagascar. Recent palaeomagnetic data from Madagascar have provided the unequivocal result that the island was situated off East-Africa near Kenya and Tanzania. The predrift relationship of eastern and western Gondwanaland established previously on morphological grounds has now been verified from the palaeomagnetic data. Palaeomagnetic data for the Mesozoic of Australia have also long been considered anomalous within the framework of Gondwanaland. The data were inconsistent with any form of reconstruction from the geological and morphological viewpoints. However, a new investigation of Mesozoic rocks in Australia has resolved that anomaly and the existence of a single group of palaeomagnetic poles for the Triassic—Jurassic of all continents comprising Gondwanaland confirms that the Smith-Hallam reconstruction is as realistic a model as currently available. The Smith-Hallam model has been used to combine palaeomagnetic data from the Gondwana continents for the Late Palaeozoic and Mesozoic. The large amount of data for the Late Palaeozoic and Early Mesozoic of South America clearly implies that the supercontinent was drifting during that period and the data are best considered in ‘time groups’ that cross Period boundaries. The unity of Gondwanaland has been confirmed until mid-Jurassic time.

Some Aspects of Plant Geography of the Northern Hemisphere During the Late Cretaceous and Tertiary

Some Aspects of Plant Geography of the Northern Hemisphere During the Late Cretaceous and Tertiary

Tetrapods and Continents

The affinities of modern land-living animals are intimately related to the positions and connections of continents, a fact nicely demonstrated by mammalian faunas throughout the world. The zoogeography of modern mammals has roots in the various distributions of mammals during Cenozoic time. In the Paleozoic and Mesozoic eras, the relationship between continental positions and tetrapod faunas is reflected by the distributions of extinct amphibians and reptiles. The early Triassic Lystrosaurus fauna, an example of this, originally described from South Africa, is now known in Antarctica, in peninsular India, and in western China. The distributions of this ancient tetrapod fauna, as well as of other later Mesozoic faunas, indicate that the regions in which they now occur were then intimately associated, allowing for the ready intermigrations of land-living vertebrates. This lends strong support to the theory of Gondwanaland, which supposes the southern hemisphere continents plus peninsular India to have been joined into a single supercontinent (the correlative theory of Laurasia supposes a similar connection of northern hemisphere continents), and to the theory of continental drift, which visualizes eventual fragmentation of these supercontinents, the fragments drifting throught time to the positions occupied by the modern continents. The changing relationships of continents due to the break-up of Pangaea (Gondwanaland plus Laurasia) and the drift of the great continental blocks to their present positions, presumably resulted in the shift of tetrapod faunas from the ancient pattern of northern and southern moieties, through intermediate conditions, seen in the dinosaurian faunas of middle and late Mesozoic time, to the zoogeographical distributions of Cenozoic mammals.

Relationship of isotopic temperatures and faunal realms to Jurassic—cretaceous paleogeography, particularly of the South-west pacific

Two major faunal realms, Boreal and Tethyan, may be recognised in Jurassic and Cretaceous macro-faunas. In the Jurassic, Boreal faunas populated the countries adjacent to the modern Arctic Ocean and penetrated southwards to about 50°N. Tethyan faunas populated the Mediterranean and Indo-Pacific regions and penetrated as far south as 75°S. Continental drift, faunal, and isotope studies suggest that, in the Jurassic, Boreal faunas were related to a cool-temperate climatic zone, developed adjacent to the Jurassic North Pole, and Tethyan faunas to a tropical and subtropical zone. A Southern Hemisphere equivalent of the Boreal Realm is not evident in the Jurassic, suggesting that at this time the Southern Hemisphere continents were grouped away from the South Pole. In the Cretaceous, a Boreal Realm can be distinguished, similar in geographic extent, and to judge from oxygen isotope data, also similar climatically to the Jurassic Boreal Realm. But the Cretaceous Tethyan Realm, again probably populated by tropic...

Critique of Hypothesis of Continental Drift--Discussion: Evidence for Continental Drift: DISCUSSION

Critique of Hypothesis of Continental Drift--Discussion: Evidence for Continental Drift: DISCUSSION

Upper Jurassic Fossils from Ellsworth Land, West Antarctica, and notes on upper Jurassic Biogeography of the South Pacific Region

Abstract Fossils from Lyon Nunataks (74° 52′ S, 74° 02′ W) are described: Conodicoelites spp., Rotularia sp. indet., indet. pectinacean: cf. Entolium, and Variamussium lyonensis sp. nov. Upper Jurassic (?Lower Kimmeridgian) age. The Conodicoelites spp. have strong affinities with those of the New Zealand Lower Kimmeridgian. Ammonites, belemnites, and Inoceramus, all with strong Indo-Pacific affinities, are present in the Kimmeridgian and Lower Tithonian of Central and South America, and the Lyon Nunataks fossils appear to be a southerly extension of this fauna. These fossil occurrences strongly suggest that a trans-Pacific migration route, probably skirting Antarctica, was available in Kimmeridgian and Lower Tithonian times. Faunal movements along this southern route are discussed in terms of: (1) Migration across existing oceans; (2) Migration between existing land masses, aided by connecting shelf areas; (3) Migration skirting formerly contiguous land masses. Continental drift is seen as a means of providing shallow-water migration routes between New Zealand, West Antarctica, and South America. Various continental reconstructions are considered, and one first published by King (1958) is preferred. Oxygen-isotope paleotemperature determinations indicate that in the Jurassic New Zealand had a temperate climate and was probably in middle latitudes, either close to its present position or in an equivalent position as part of Gondwanaland. Two major faunal realms, Boreal and Tethyan, developed in the later half of the Jurassic. The boundary between the two realms is thought to have been essentially climatically controlled, the Boreal faunas probably consisting of temperate or cooltemperate stenothermal animals, and the Tethyan faunas and derivatives warm or warm-temperate stenothermal. In the late Jurassic, differentiation within the Tethyan realm, perhaps as a result of short-term orogenic barriers, allowed the evolution of distinct Indo-Pacific faunas. The relationship of the West Antarctic fossils to these faunal groupings is discussed. The geographic distributions of the Jurassic faunas are considered in relation to both present-day latitudes and to paleolatitudes determined from paleomagnetic and continental drift studies. The apparent absence of a Southern Hemisphere equivalent of the Boreal realm raises the question whether the Southern Hemisphere continents may. have been grouped away from the Jurassic South Pole. Northern Hemisphere contments on the other hand may have been grouped close to the Jurassic North Pole. This factor, as well as perhaps improved oceanic circulation in the Southern Hemisphere, may have allowed Tethyan and related faunas to populate latitudes in the Southern Hemisphere that in the Northern Hemisphere were populated by Boreal faunas.

Tectonics of Antarctica: ABSTRACT

Antarctica has long been considered to consist simply of a large Precambrian shield, flanked on one side by the circum-Pacific belt of Mesozoic and Cenozoic orogeny. The great amount of geologic information obtained during recent years indicates that between shield and circum-Pacific belt are belts of Paleozoic orogeny. The continent is probably crossed by a late Precambrian and Early Cambrian miogeosyncline whose contents were metamorphosed and intruded by batholiths during the Middle (?) Cambrian. Erratics bearing Lower Cambrian pleosponges, like those characterizing the Adelaide geosyncline of South Australia, have been found in four places; K/Ar dates suggest crystallization about 500 million years ago; and the distinctive granites are remarkably similar to those of Middle Cambrian age in South Australia. This orogen crosses the Antarctic coast between 145° and 160° E., and flanks the Ross Sea and Ross Ice Shelf, and possibly Filchner Shelf and Weddell Sea, as a continuous system of high mountains. These mountains have long been termed the Great Antarctic horst, thought to be of old P ecambrian rocks; the horst concept was based on a misinterpretation of structures near McMurdo Sound, where the broad structure of the present range is anticlinal. At least in the 1,100-mile segment from Terra Nova Bay to the Horlick Mountains, the crystalline rocks are metasedimentary rocks whose structures are subparallel with the mountain system, and distinctive granitic rocks of a composite batholith. Rocks of the orogen are overlain by little-deformed Devonian to Triassic sedimentary strata. Northeastern Victoria Land, west of the Ross Sea, is composed of metasedimentary rocks, striking generally west-northwestward, whose metamorphism and intrusion by granites occurred about 350-400 million years ago. On strike across the Ross Sea, and trending toward the Weddell Sea at least to the region of 90° W., 82° S., are metasedimentary rocks intruded by distinctive granites which contain relatively large trace amounts of tin. These rocks are undated, but are unlike the Mezozoic crystallines of Palmer Peninsula; a middle Paleozoic age is likely. It may be significant that Devonian granites of eastern Australia are also relatively rich in tin. The coast between 35° and 165° E. is characterized by charnockites, granulites, and gneisses, in part polymetamorphic, and by varied younger crystalline rocks. The rocks resemble those of the Precambrian K/Ar ages. As has long been recognized, this is part of a Precambrian shield, which may extend farther toward the Weddell Sea, and which presumably extends far toward the South Pole also. The Palmer Peninsula belongs to the circum-Pacific orogen, as has long been known, and the Thurston Peninsula also may belong to it. This revised pattern of Antarctic tectonics is essentially that required by Du Toit's reassembly of the southern hemisphere continents before post-Paleozoic continental drift. End_of_Article - Last_Page 408------------