Letteratura scientifica selezionata sul tema "Paleobiogeography - Australia"

Cambrian malacofauna of Australia is among the most taxonomically diverse among time equivalents. By a number of valid mollusc species Australian Cambrian competes with Siberian and Chinese formations. Up to date, 80 valid species and 12 forms in open nomenclature, apparently representing new undescribed taxa, have been recorded from the Lower–Middle Cambrian successions of Australia. In addition, 6 species names can be considered as junior synonyms. Distribution ranges of mollusc species plotted over the modern stratigraphic scheme reveal four major molluscan evolutionary assemblages in the interval of Tommotian–Undillan stages. In paleogeographic aspect, the Cambrian malacofauna of Australia has 29 species in common with Siberian Platform, Kazakhstan, Altai-Sayan, Transbaikalia, Mongolia, South and North China, Morocco, Antarctic, Europe (Denmark, Germany), Greenland, North America, and New Zealand, providing important correlation links between these regional stratigraphic schemes.

Abstract. A variety of paleogeographic atlases have been constructed, with applications from paleoclimate, ocean circulation and faunal radiation models to resource exploration; yet their uncertainties remain difficult to assess, as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing paleogeographic maps, by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to compare a Phanerozoic Paleogeographic Atlas of Australia with biogeographic indicators. The agreement between fossil data and paleogeographic maps is quite good, but the methodology also highlights key inconsistencies. The Early Devonian paleogeography of southeastern Australia insufficiently describes the Emsian inundation that is supported by biogeography. Additionally, the Cretaceous inundation of eastern Australia retreats by 110 Ma according to the paleogeography, but the biogeography indicates that inundation prevailed until at least 100 Ma. Paleobiogeography can also be used to refine Gondwana breakup and the extent of pre-breakup Greater India can be inferred from the southward limit of inundation along western Australia. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.

Paleobiogeography will play an important role in furthering our understanding of global change, particularly with respect to providing constraints on past climates. As a result of this there is increasing emphasis within the paleontological community on the past spatial distributions of faunas, extinctions, and originations. Thus there is an increasing interest in reconstructions of the past distributions of continents, so that maps and paleo-latitudes of faunas, extinctions or originations can be determined. This results in an increasing need to understand the state of the art of global plate reconstructions through the Mesozoic and Cenozoic, and global continental reconstructions through the Paleozoic, i.e. what we know and how well do we know it. The talk will summarize our present understanding of Mesozoic and Cenozoic plate motions using computer animations followed by a brief summary of the present understanding of individual continental apparent polar wander paths (APWP's) as well as motions in the global frame. Global and continental mean poles at approximately 20 Ma intervals have been computed for all of the major continents of the Phanerozoic using data from Van der Voo (1992) and plate motions derived from a detailed analysis of Mesozoic and Cenozoic seafloor spreading data. Comparison of mean continental poles reconstructed into the same reference frame shows that although there is general agreement, statistically different pole positions are quite commonly observed. This is particularly true for the Late Cretaceous and pre-Late Jurassic of the northern Hemisphere, and has resulted in some controversy concerning appropriate Atlantic fits. The differences in predicted (or reconstructed) paleo-latitudes are not trivial, particularly for areas of esatern Gondwanaland such as Australia and New Zealand, and are not easily visualized from a simple comparison of mean pole positions. A final focus will be with regards to reconstructions of Asia. Comparison of recently published Permian global reconstructions in the McKerrow and Scotese (1989) volume demonstrates that vast differences of interpretation persist and that paleontologists among others cannot accept exisiting reconstructions uncritically.

Jurassic–Cretaceous ammonites are particularly robust fossil tools in global stratigraphy and correlation. The successive evolution and extinction of these cephalopod mollusks was so rapid that many ammonite zones are no more than one million years in duration. A well-preserved ammonite specimen from the Fortissimo-1 core, Browse Basin, NW Australia is assignable to the widespread latest Jurassic dimorphic berriaselline genus, Blanfordiceras Cossmann, recorded previously from the Spiti area, Nepal, Tibet, Madagascar, Papua-New Guinea, Antarctica, and southern South America. This is the first report of ammonites of this age in the Australian region. The evolute shell of an estimated 90-100 mm diameter (when extrapolated) and pronounced ornamentation of variably bifurcating, curvilinear and flexuous ribs, intercalated with simple, non-bifurcating ribs, is consistent with Blanfordiceras wallichi (Gray, 1832), which has traditionally been restricted to the uppermost Tithonian Stage, ca. 146.5-145.5 Ma, but may well have survived into the earliest part of the Berriasian. The first recorded occurrence of this ammonite in Australia fills an anomalous absence in the paleobiogeographic distribution of Jurassic–Cretaceous boundary ammonites in the Indo-SW Pacific Subrealm with important implications for the calibration of offshore rocks and wells in Australia.

It has often been assumed that the intensively studied dinosaur faunal assemblages of western North America and the Gobi Desert of Mongolia and China represent “typical” Late Cretaceous terrestrial vertebrate communities. This assumption has led to a paleoecological scenario in which a global ecological shift occurs from the dominance of high-browsing saurischian (i.e., sauropod) to low-browsing ornithischian (i.e., iguanodontian, marginocephalian, ankylosaurian) herbivore communities. Furthermore, the assumption that the Asiamerican dinosaur faunas are communities “typical” of the Late Cretaceous has forced the conclusion that the sauropod-dominated Argentine population must have been an isolated relict ecosystem of primitive taxa (i.e., titanosaurid sauropods, abelisaurid ceratosaurs). Recent discoveries and reinterpretations of other Late Cretaceous assemblages, however, seriously challenge these assumptions.Paleogeography and paleobiogeography have demonstrated that terrestrial landmasses became progressively fractionated from the Late Jurassic (Kimmeridgian-Tithonian) to the Late Cretaceous (Campanian), owing to continental drift and the development of large epicontinental seas (the Western Interior Seaway, the Turgai Sea, etc.). The Maastrichtian regressions resulted in the reestablishment of land connection between long isolated regions (for example, western and eastern North America). These geographic changes are reflected in changes in the dinosaurian faunas. These assemblages were rather cosmopolitan in the Late Jurassic (Morrison, Tendaguru, and Upper Shaximiao Formations) but became more provincialized throughout the Cretaceous.Cluster analysis of presence/absence data for the theropod, sauropod, and ornithischian clades indicates that previous assumptions for Late Cretaceous dinosaurian paleoecology are largely in error. These analyses instead suggest that sauropod lineages remained a major faunal component in both Laurasia (Europe, Asia) and Gondwana (South America, Africa, India, and Australia). Only the pre-Maastrichtian Senonian deposits of North America were lacking sauropodomorphs. Furthermore, the abelisaurid/titanosaurid fauna of Argentina is, in fact, probably more typical of Late Cretaceous dinosaurian communities. Rather, it is the coelurosaurian/ornithischian communities of Asiamerica (and particularly North America) that are composed primarily of dinosaurs of small geographic distribution. Thus, the Judithian, Edmontonian, and Lancian faunas, rather than being typical of the Late Cretaceous, most likely represent an isolated island-continent terrestrial vertebrate population, perhaps analogous to the extremely isolated vertebrate communities of Tertiary South America. Furthermore, the shift from high-browsing to low-browsing herbivore “dynasties” more likely represents a local event in Senonian North America and does not represent a global paleoecological transformation of Late Cretaceous dinosaur community structure.

Articulate brachiopods from the Aptian–Coniacian (Kotick Point and Whisky Bay Formations, Gustav Group) and the Santonian–Campanian (Santa Marta Formation, Marambio Group) of James Ross Island are described. A new terebratulid species,Rectithyris whiskyin. sp., is described from the late Albian–early Coniacian of the Whisky Bay Formation. The record from the late Albian is supported by palynological evidence making it contemporaneous with other species ofRectithyrisfrom Europe. The relative abundance ofRectithyris whiskyin. sp. in late Turonian to early Coniacian sections indicates an extended biohorizon that may aid biostratigraphic correlation in the James Ross Island region.The brachiopods have some affinities with faunas described from Europe, northern Siberia, North America, Madagascar, southern India, Western Australia, and Alexander Island, Antarctic Peninsula. Elements of the James Ross Island brachiopod fauna probably migrated by the following routes: 1) from northern high latitudes via the Eastern Pacific; 2) from Europe via the north and central Atlantic and opening south Atlantic Ocean; and 3) via Eastern Tethys, the East African Seaway, to the south Atlantic Ocean. Brachiopod evidence supports a fully marine connection between the central Atlantic and south Atlantic Ocean (Route 2) possibly as early as the late Albian (as do ammonite faunas from western Africa), and certainly by the late Turonian. Route 3 was established in the Cretaceous by the Aptian?–Albian to eastern Africa and Madagascar and to the Antarctic Peninsula by the late Turonian. Faunal links between James Ross Island and Western Australia support the Late Cretaceous juxtaposition of these plates.A distinct austral brachiopod fauna may be present in the Cretaceous from the Aptian onwards (although current evidence is scant). Antarctic Peninsular and Western Australian faunas yield five brachiopod genera (and their species) endemic to Gondwanaland's southern marine fauna. Other genera known from the Antarctic Peninsula (Kingena, Ptilorhynchia, andRectithyris) and the Northern Hemisphere may have species endemic to Gondwanaland.

AbstractThe bryozoan fauna from the South American Cenozoic is poorly known. The study of new material collected in the Monte León Formation (early Miocene), gave us the opportunity to describe four new species: Valdemunitella canui n. sp., Foveolaria praecursor n. sp., Neothoa reptans n. sp., and Calyptotheca santacruzana n. sp. Two of them (V. canui and C. santacruzana) were first recorded by F. Canu and interpreted as recent species from the Australian bryozoan fauna, but are herein described as new species. The stratigraphic range of Otionella parvula (Canu, 1904) is extended to the early Miocene. The present study emphasizes the close relationships between the South American Neogene bryozoan faunas and those of other Gondwanan sub-continents such as New Zealand and Australia.

A middle Cenomanian faunule from the Moonkinu Formation of Bathurst Island in Northern Australia contains the best-preserved suite of benthic Mollusca known from the Cretaceous of the Australian region. Twenty-four species of bivalves, gastropods, and scaphopods, many exquisitely preserved with original aragonitic nacre, are recognized. Thirteen are new: Nucula s.l. meadinga n. sp. (Nuculidae), Nuculana bathurstensis n. sp. (Nuculanidae), Jupiteria? n. sp. A (Nuculanidae), Varicorbula cretaustrina n. sp. (Corbulidae), Vanikoropsis demipleurus n. sp. (Vanikoridae), Euspira n. sp. A (Naticidae), Amuletum praeturriformis n. sp. (Turridae), Granosolarium cretasteum n. sp. (Architectonicidae), Echinimathilda moonkinua n. sp. (Mathildidae), Acteon bathurstensis n. sp. (Acteonidae), Biplica antichthona n. sp. (Ringiculidae), Goniocylichna australocylindricata n. sp. (Cylichnidae), and Dentalium (Dentalium) n. sp. A (Dentaliidae). Nominal species of Nuculana, Grammatodon, Cylichna, and Laevidentalium also are present. The occurrence of ammonites, including taxa that occur in the type Cenomanian, securely establishes the fauna as middle Cenomanian (Acanthoceras rhotomagense Zone). The Moonkinu Formation and its faunule were deposited in a high-energy, shallow-shelfal setting, as part of a large-scale regressive cycle recognized as the Money Shoals Platform of northern Australia. The assemblage represents a parauthochthonous suite which experienced little or no post mortem transport. Epifaunal and infaunal suspension feeders (some 60 percent) dominate the bivalve fauna with a subordinate representation of deposit-feeding infaunal burrowers (some 40 percent). Nearly all of the gastopods were carnivores with the aporrhaid Latiala mountnorrisi (Skwarko), probably a deposit feeder, the only exception. The scaphopods were probably micro-carnivores. Concentrations of the ammonite Sciponoceras glaessneri are likely the result of mass kills in surface waters. The cosmopolitan nature of the Bathurst Island fauna at the genus-level reflects unrestricted oceanic circulation patterns and an equitable climate on a global scale during the Cenomanian. The retreat and disappearance of the Australian epicontinental sea at the close of the Albian coincided with reduced endemism in the molluscan faunas, after which time the continental shelves hosted a rich suite of cosmopolitan affinity. The high number of endemic species in the Moonkinu Formation probably represents an early stage of broad-scale genetic separation among Southern Hemisphere molluscan stocks, a trend that became increasingly pronounced through the Late Cretaceous. The new records of Varicorbula, Amuletum, Granosolarium, Echinimathilda, and Goniocylichna represent the oldest occurrences recorded for these genera and are suggestive of Southern Hemisphere origins.

It is widely believed that Australian Aboriginals utilised fire to manage various landscapes however to what extent this impacted on Australia???s ecosystems remains uncertain. The late Pleistocene/Holocene fire history from three sites within the Sydney Basin, Gooches Swamp, Lake Baraba and Kings Waterhole, were compared with archaeological and palaeoclimatic data using a novel method of quantifying macroscopic charcoal, which is presented in this study. The palynology and other palaeoecological proxies were also investigated at the three sites. The Gooches Swamp fire record appeared to be most influenced by climate and there was an abrupt increase in fire activity from the mid-Holocene perhaps associated with the onset of modern El Ni??o dominated conditions. The Kings Waterhole site also displayed an abrupt increase in charcoal at this time however there was a marked decrease in charcoal from ~3 ka. Lake Baraba similarly had displayed low levels of charcoal in the late Holocene. At both Kings Waterhole and Lake Baraba archaeological evidence suggests intensified human activity in the late Holocene during this period of lower and less variable charcoal. It is hence likely that at these sites Aboriginal people controlled fire activity in the late Holocene perhaps in response to the increased risk of large intense fires under an ENSO-dominated climate. The fire history of the Sydney Basin varies temporally and spatially and therefore it is not possible to make generalisations about pre-historic fire regimes. It is also not possible to use ideas about Aboriginal fire regimes or pre-historic activity as a management objective. The study demonstrates that increased fire activity is related to climatic variation and this is likely to be of significance under various enhanced Greenhouse scenarios. There were no major changes in the composition of the flora at all sites throughout late Pleistocene/Holocene although there were some changes in the relative abundance of different taxa. It is suggested that the Sydney Sandstone flora, which surrounds the sites, is relatively resistant to environmental changes. Casuarinaceae was present at Lake Baraba during the Last Glacial Maximum and therefore the site may have acted as a potential refugium for more mesic communities. There was a notable decline in Casuarinaceae during the Holocene at Lake Baraba and Kings Waterhole, a trend that has been found at a number of sites from southeastern Australia.

This thesis presents a pollen analytical reconstruction of mallee vegetation history in the vicinity of Lake Tyrrell, a large active salt lake in semi-arid northwestern Victoria. The project combined studies of the modern pollen rain, pollen depositional processes and sedimentological characteristics of lake deposits to provide an analytical framework appropriate to the interpretation of fossil pollen spectra from the novel salt lake setting. Pollen trapping in northwestern Victoria and western New South Wales indicates that the characteristic plant communities of semi-arid southeastern Australia can be identified from the pollen spectra they produce. Mallee heath communities produce spectra containing a diverse array of heathland taxa with limited pollen dispersal capacities, including Banksia, Baeckea behrii, Cryptandra and Calytrix tetragona. Mallee heaths also produce large amounts of Calli tris pollen but can be distinguished from Callitris woodland by the regular presence of pollen from restricted heathland taxa. Pollen spectra from chenopod shrublands are characterised by overwhelming dominance by Chenopodiaceae pollen. Other halophytic taxa often represented include Selenothamnus and Disphyma. Riverine forests produce pollen spectra dominated by Eucalyptus Muehlenbeckia cunninghamii and Amyema pollen occur commonly. It may be possible to identify pollen of Eucalyptus camaldulensis in fossil assemblages allowing this community to be more clearly delineated in the fossil record. Mallee communities can be distinguished from eucalypt dominated communities in moister areas by producing pollen spectra containing relatively high percentages of chenopod pollen and low percentages of grass pollen. Eucalypt woodlands in areas receiving more than 400 mm mean annual rainfall produce pollen spectra containing appreciable quantities of Callitris pollen. No relationship could be discerned between pollen production and rainfall in this study. Pollen trapping at Lake Tyrrell suggests that the majority of pollen arriving at the lake surface is wind borne. Few are washed from the lake margin or imported down Tyrrell Creek. This contrasts strongly with the situation in humid areas where pollen washed from the catchment or carried in creeks are a significant part of a lakes pollen budget. Pollen reaching the surface of Lake Tyrrell are rapidly redistributed and are preferentially deposited in areas marginal to the persistent salt crust. Maximum pollen concentrations occur on relatively high parts of the lake bed, again contrasting strongly with models derived from permanently wet lakes where maximum deposition of pollen occurs in the deepest parts of the basin. The sediments of Lake Tyrrell record a history of hydrological change extending to approximately 10,000 BP. Between 10,000 BP and 6600 BP water in Lake Tyrrell was shallow, saline and probably ephemeral. Water depths and the frequency I duration of flooding were most likely similar to those experienced today but there was no persistent salt crust. Between 6600 BP and 2200 BP the lake was a permanent though fluctuating waterbody. The lake waters were saline throughout this period. Water balance calculations suggest average rainfall in the lake catchment would have been approximately 2.6 times modern levels between 6600 BP and 2200 BP. The lake was dry between 2200 BP and 800 BP. The local groundwater table fell below the lake bed. There was no salt crust until about 800 BP when rainfall increased slightly allowing local watertables to rise and modem salt lake conditions to develop. Changes in vegetation around Lake Tyrrell occur in association with changes in rainfall. Between 10,000 BP and 6600 BP Lake Tyrrell was surrounded by open woodland dominated by Allocasuarina Eucalyptus and Callitris were probably present in limited areas. At 6600 BP mallee communities began to dominate the landscape. It is likely the appearance of mallee reflects the arrival of mallee eucalypts spreading from refugial areas occupied during the last glacial maximum. Callitris patches were a prominent element of the regional vegetation during this the wettest interval in the Holocene record. They appear little affected by the active fire regime of the times. Between 2200 BP and 800 BP mallee persisted and Allocasuarina experienced a modest expansion. Callitris declined drastically. The dense mallee vegetation which surrounded the lake at the time of European settlment was established after 800 BP. The history of Holocene environmental change identified from Lake Tyrrell provides a possible explanation for the patterns of archaeological site distribution observed in the Mallee Districts of northwestern Victoria.