Palaeogeographic Maps Research Articles

Late palaeozoic and mesozoic palaeogeography of Southeast Asia

Southeast Asia comprises a complex assemblage of allochthonous terranes derived directly or indirectly from Gondwana Land and assembled between the Late Palaeozoic and Cenozoic. The continental “core” of the region is made up of four principal continental blocks, South China, Indochina, Sibumasu and East Malaya. South China, Indochina and East Malaya were rifted from northeast Gondwanaland during the Silurian or Devonian and amalgamated to each other during the early Carboniferous. Sibumasu remained attached to northwest Australian Gondwana land until the late early Permian when it rifted away as part of the elongate Cimmerian continent. Collision between Sibumasu and Indochina-East Malaya probably occurred in the early Triassic forming the continental core of Southeast Asia. Other small terranes including Mount Victoria Land, Sikuleh, Natal, Semitau and southwest Borneo were accreted to this core during the Jurassic and Cretaceous to form “Sundaland”. A series of palaeogeographic maps are presented showing interpreted palaeopositions of the various Southeast Asian terranes in the Late Palaeozoic and Mesozoic which are consistent with the current geological and geophysical constraints.

Aptian-Albian palaeogeography of Neo-Tethyan domain

The Aptian-Albian interval (124.5-97.0 Ma) was a critical time both globally and for the Tethyan domain. In the Tethyan domain it was the time when a united Neo-Tethyan subduction zone became established between the future site of the Alps and Southeast Asia and greatly accelerated the rate of north-south convergence throughout the Tethyan region. A consequent widespread transgression on both Laurasian and Gondwanian margins deposited Orbitolina limestones and associated clastics on wide continental shelf areas. On the sea-floor of the Neo-Tethys ocean, organic-rich siliceous black shales, radiolarites, and turbidites with minor amounts of carbonates were deposited. Siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the Neo-Tethyan realm and along their margins. These areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves. Following the establishment of the north-dipping subduction zone, the Laurasian passive margin was largely converted to an active one, fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin. Land areas and continental basins were widespread on this margin in northern Tibet, China and Indo-China. This was a consequence of the Late Triassic to Early Jurassic continental collissions and accompanied intracontinental convergence that lasted well into the Cretaceous. A detailed Aptian-Albian facies map and a crude palinspastic palaeogeographic map of the entire Tethyan realm are prepared in order to express the contrasts in sedimentation on Laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in Tethysides.

Milankovitch and albedo forcing of the tropical monsoons: a comparison of geological evidence and numerical simulations for 9000 yBP

ABSTRACTLake-level and palaeoecological evidence from Africa, Arabia and southern Asia for 9000 yBP suggests an intensification and increased poleward penetration of the northern monsoons. The vegetation belts shifted north by 4–6° latitude on the south side of the Sahara. In contrast, the monsoon over southern Africa was weaker than today. Calculations based on the new palaeogeographical map of Mali by Petit-Maireet al.(1988) indicated that the areaaveraged surface albedo decreased by 0·10–0·14 in the zone 16–24°N and that total annual precipitation increased by 150–320 mm north of the inland delta of the Niger (20–24° 15′N). Experiments with atmospheric general-circulation models suggest that this asymmetrical pattern of anomalies in the strength of the tropical monsoons can be explained in broad terms by the different orbital configuration of the Earth at 9000 yBP. Here, we describe a hitherto unpublished sensitivity experiment with the low-resolution (5° × 7·5°) version of the U.K. Meteorological Office 11-layer model, in which the albedo over Africa and Arabia between 15 and 30°N was reduced by between 0·04 and 0·06 to simulate the increase in vegetation cover at 9000 yBP. The results indicate that the surface-albedo change provides a significant positive feedback enhancing the direct climatic effects of Milankovitch forcing in the tropics.

The Silurian and Early Devonian biogeography of ostracodes in North America

Abstract Silurian and Early Devonian ostracode associations in North America represent at least three ecotypes, a leperditicopid association, a large beyrichiacean association, a mixed association, and possibly a fourth, spinose podocopid association, or Thuringian ecotype. Comparison of the large beyrichiacean association and mixed association ecotypes indicates the presence of three informal ostracode provinces, the Appohimchi, Baltic-British and Cordilleran, which remained relatively constant in geographical position throughout the Silurian and Early Devonian. Plotting the provinces on palaeogeographic maps suggests that temperature was not an important factor in delimiting the provinces, and land barriers, or possibly deep-water troughs as barriers, were the cause of provincial development. Benthic ostracodes differed from other benthic invertebrates such as brachiopods and corals in developing provincialism in the late Llandovery and having it start to decline in the Pragian through the Emsian.

Early and Middle Devonian gastropod biogeography

Abstract Early and Middle Devonian gastropods show biogeographic patterns remarkably similar to those of better studied faunal groups of this same interval, notably articulate brachiopods, rugose corals, and trilobites. Three biogeographic realms are recognized: Old World, Eastern Americas, and Malvinokaffric Realms. Gastropod diversity is highest in the Old World Realm and lowest in the Malvinokaffric Realm. The diversity patterns and the high degree of shell ornamentation suggest that the Old World Realm was generally warmer than the Eastern Americas Realm, and that both were considerably warmer than the cool temperate to cold polar waters of the Malvinokaffric Realm. The utility of gastropods for fine-scale delineation of biogeographic units is illustrated for the Eifelian of western North America. At least two subprovincial units (the Alaska-Yukon and Nevada subprovinces) can be recognized. Eifelian gastropods from interior and southeastern Alaska belong to a single unit (the Alaska-Yukon Subprovince), and are most closely related to coeval faunas of northwestern Canada, suggesting little displacement of most of Alaska's so-called 'suspect' terranes. Plotting the data on the Devonian palaeogeographic maps of Scotese results in several suggested emendations: (1) North America should be moved south by 10-20°; (2) Australia is too far south on the Emsian and Givetian reconstructions, it should be in a more palaeotropical position; and (3) Siberia is too far north, it too should also be placed in a palaeotropical position.

The late Permian palaeogeography of north-east England

SUMMARY All available information has been used in the preparation of a series of palaeogeographical maps showing the evolution of north-east England at the end of the early Permian and at intervals throughout the late Permian. Most of the area initially lay near the western fringe of the Southern North Sea tropical desert basin, much of which was flooded at the beginning of the late Permian so as to create the epicontinental Zechstein Sea. With continually oscillating relative sea levels and episodic differential subsidence, contemporary coastlines fluctuated widely whilst successive progradational carbonate shelves were constructed in the first two of four main cyclic sequences; the deposition of thick salt at the end of the second main cycle almost filled the basin, eliminating most of the earlier depositional topography and ensuring that carbonates and evaporites of the third and fourth cycles were formed in a less diverse range of coastal plain to shallow marine environments.

Research in exploration geoscience: The AMIRA model

The paper summarises the exploration related R&D that has been managed by AMIRA/APIRA and gives details of the complex, market oriented process used to develop new projects.The process is illustrated by three case studies taken from the more than 70 exploration projects completed.The Gold Deposits of North Queensland Project conducted by James Cook University studied the various styles of gold mineralization. The Rock Magnetism project undertaken at CSIRO Division of Exploration Geoscience allowed both general and specific research themes to be undertaken in parallel with confidential proprietary investigations on sponsors' drill core. The Palaeogeographic Mapping project undertaken at the BMR Division of Continental Geology provided sponsors with palaeogeographic maps including interpretation and structural information of 70 time slices.Some of the benefits of the AMIRA/APIRA approach are discussed as well as some of the difficulties which arise in ensuring companies obtain appropriate benefits from their sponsorship.

Fossile Funde von Castanopsis (D. Don) Spach (Fagaceae) und ihre Bedeutung für die europäischen Lorbeerwälder )

Summary A synopsis is given of the fossil Castanopsis-remams in Europe. Only fruits and wood stand a critical test. Five fossil species exist from the Oligocene to the Upper Miocene in Europe. Their distribution is figured in palaeogeographical maps. The mid-Tertiary Castanopsis- taphocoenosis is developed only at edaphical acid places (browncoals, quartzites, gravels) in an antagonistic relation to the Dryophyllum – or Trigonobalanopsis – thaphocoenoses. It belongs to the Laurel-Coniferous forests.

Palaeomagnetic data, late precambrian magnetostratigraphy and tectonic evolution of Eastern China

In this paper middle and upper Proterozoic (1900-1600 Ma) APW paths are presented for North and South China based on palaeomagnetic results obtained from the Jixian, Yangzi Gorges, Shennongjia and Fuzhou areas in eastern China. Two or three “loops” are present; the second of these has an age of about 1000-800 Ma and is probably roughly equivalent to the Sveconorwegian and Grenville loops. APW paths, loops, reversed polarity zones and pole positions, combined with geological data, permit definition of several markers that are useful in regional correlation. These form the basis for a proposed stratigraphic subdivision of the middle and upper Proterozoic in China. A tentative palaeogeographic map has been drawn for the North China and Yangzi Blocks for the period from 1700 Ma to 600 Ma.

The relevance of biogeography to palaeogeographical reconstructions

I would like to discuss here the palaeogeographic maps for the late Silurian (figures 1 and 2) used by Smith et al. (1981) and by Bambach et al. (1980; essentially the same maps are used by Parrish et al. (1983)). On these two late Silurian maps I have plotted the best available late Silurian biogeographical data (Boucot 1975; Wang et al. 1984). Note that the Smith et al. (1981) maps are biogeographically untenable, that is, the surface current circulation patterns consistent with the postulated palaeogeography are unable to explain the high level endemism which is present. Additionally, note that the presence of major evaporitic bodies in an equatorial position is unlikely. By using the same approach the Bambach et al . (1980) palaeogeography for the late Silurian is rejected for the same reasons. The maps for the Lower Devonian published by both groups have been rejected earlier (Boucot & Gray 1983); the similar arguments will not be repeated here. I (Boucot, this symposium) provide pangaeic reconstructions for these time intervals which are consistent with the biogeographical and lithological information.

Orcadian Basin issue. Editorial introduction

This part of the Scottish Journal of Geology contains a group of papers relating to the geology of the Orcadian Basin. The idea for a thematic part of the Journal came from T. R. Astin who convened the Orcadian Basin Meeting held at Cambridge in September, 1984. The majority of the papers in this part were presented at the Cambridge meeting. The meeting provided a timely forum for a variety of perspectives on the Orcadian Basin. The term Orcadian Basin is generally used with reference to the exposures of Old Red Sandstone (ORS) from the southern shores of the Moray Firth, westwards to the Inverness area and north to Caithness, Orkney and Shetland. The eastern margin of the Orcadian Basin lies offshore and cannot be defined. Palaeogeographic maps with the Orcadian Basin labelled as extending from Scotland to Norway ([Ziegler 1982][1]) give a very simplified impression of ORS sedimentation. Throughout the area numerous depocentres probably existed; each of which could have received combinations of Lower, Middle and Upper ORS fill. Mykura ([1983][2]) gives a general account of the ORS of the Orcadian Basin which would introduce the reader to the papers in this issue. Details of stratigraphy are given by [Westoll (1977)][3]. Subsidence areas and structural style vary considerably between Lower, Middle and Upper ORS. Several Lower ORS basin depocentres existed (Parnell; Richards) and deformation and faulting affected these rocks prior to deposition of the Middle ORS sequence. The thick dominantly lacustrine, Middle ORS sequence is seen to have greater . . . [1]: #ref-5 [2]: #ref-2 [3]: #ref-4

Palaeocontinental configurations and geoid anomalies

Reconstructions of past continental configurations help our understanding of the evolution of planetary surface morphology and impose valuable constraints on the models for planetary dynamics. The problem is that although well established palaeogeographical maps now exist for Mesozoic and later times1,2, thanks to excellent agreement between palaeomagnetic and marine-magnetic deductions, this is not true for earlier times mainly due to the lack of independent palaeogeophysical control over otherwise longitudinally-ambiguous palaeomagnetic data. The prospect of relating palaeocontinental configurations to geoid anomalies, recently raised by Anderson3, has thus given a fresh perspective to this problem. Here his continental insulation model is shown to be an inadequate explanation of the undulations of subduction-compensated geoid. Instead, the geoid highs and lows are shown to correlate well with the overall divergent and convergent plate tectonism since the middle Palaeozoic and are thus ascribed, respectively, to the ascending and descending patterns of lower-mantle convection.

Fragmentation and assembly of the continents, Mid-carboniferous to present

Eighteen maps showing the motions of the major continents following the break-up of Wegener's Pangaea in the Early to Mid-Jurassic are presented. Palaeolatitudes are determined palaeomagnetically, palaeolongitudes mainly from sea-floor spreading evidence. The break-up commences with the opening of the southern North Atlantic in the mid-Jurassic and its extension north and south in the Cretaceous and Cenozoic. Concurrently the northern continents move northwards away from the southern continents (Gondwana) and a continuous east-west seaway is formed between them in the Cretaceous. Successive fragmentation of continents then created the Arctic, Indian and Antarctic Oceans. Five maps showing the disposition of land in the Permian are also given. These are based on the palaeomagnetic evidence and the idea of minimizing the motions required to bring the continents into their known Early Jurassic configuration. The Permian maps show Gondwana situated further east than in the Pangaea configuration of Wegener. There are severe problems in constructing palaeogeographical maps for the Triassic and none are presented. Palaeomagnetic results from smaller crustal fragments are also reviewed and the evidence for the former dismemberment of Eurasia and the western part of the North American cordillera are set out. The results indicate that most orogenies are to some degree collisional in nature.

THE CAMBRIAN PALAEOGEOGRAPHY OF AUSTRALIA AND OPPORTUNITIES FOR PETROLEUM EXPLORATION

As part of a larger project to re-evaluate the petroleum potential of Australia, it was considered necessary to produce a series of Cambrian palaeogeographic maps. This required the compilation and correlation of a large number of stratigraphic columns, the delineation of sedimentologlcally-significant time intervals, the production of data maps for these same time intervals, and the development of a Cambrian 'tectonic' map. This palaeogeographic study was not undertaken to establish precise exploration targets. However, it does provide new information on where many of the essential components are, what age they are, and why they are there, and as such is a valuable tool in the overall exploration and resource evaluation strategy.The six palaeogeographic maps finally produced illustrate events involving continental drift, tectonics, and climatic and sea-level variations, over a period of 70 million years. Together, these events produced marked changes in the palaeogeography and depositional environments, which in turn profoundly affected the type and distribution of sediments being deposited on and around the palaeo-continent during the Cambrian. Using the palaeogeographic maps and the data accumulated for the project, it is possible to demonstrate that organic-rich sediments, with the potential to be petroleum source rocks, were relatively common during the Cambrian, especially on the eastern cratonic margin during the Lower Cambrian (Officer and possible Amadeus Basins) and the Middle Cambrian (Georgina Basin). There may also be some suitable petroleum source rocks in the Ord Basin. Limestones and dolomites, some of which may constitute potential reservoir rocks, were deposited in a number of Cambrian intracratonic basins (Amadeus, Georgina Basins) and on the shelf (Cooper Basin). Cambrian sandstones in Australia are commonly poor reservoir rocks, but where they have been subjected to shore-line or shelf 'clean-up', for example during the Middle and Upper Cambrian on the northwest side of the craton (Bonaparte Gulf Basin), there may be some potential reservoir rocks. Some sandstones may also be present on the south side of the Cooper Basin. Fine-grained impermeable sediments (potential cap rocks) were deposited throughout the Cambrian, but evaporites were most common during the Early and lower Middle Cambrian. Synsedimentary tectonics may have produced structural and stratigraphlc traps, and a major phase of karsting occurred in the Cambrian. Therefore, the Cambrian of Australia is believed to have many of the prerequisites for the generation, migration and entrapment of hydrocarbons. Especially favourable areas for these features may lie to the southeast of the Georgina Basin and in the offshore region northwest of the Ord and Bonaparte Gulf Basins.

History of the Ross Sea region during the deposition of the Beacon Supergroup 400 - 180 million years ago

Abstract The Beacon Supergroup is the generally flat-lying sedimentary sequence about 2½km thick that rests unconformably on Ordovician and older rocks of the East Antarctic craton. In the Ross Sea region exposure is almost entirely limited to the Transantarctic Mountains, though Devonian rocks are now known from Marie Byrd Land. The history of the region is summarised on five palaeogeographic maps using a chronology based on palynomorphs but with help from several other fossil groups and the simple lithostratigraphy. However, the time-transgressive nature of the stratigraphy is recognised from the appearance of volcanic debris in the Permian at successively higher levels down the palaeoslope. The persistent feature of sedimentation during Beacon times is the development of elongate sedimentary basins sited along the present Transantarctic Mountains. Then the eastern Ross Sea and Marie Byrd Land were similar in elevation to the East Antarctic craton on the other side of the Beacon basins, from which it is...

Wenlock stratigraphy and palaeogeography of Wales and the Welsh Borderland

The description of brachiopod communities in the Wenlock of Wales and the Welsh Borderland permits interpretation of local marine environments. Graptolites and evolving lineages of brachiopods (notably Resserella sabrinae subspecies) allow the beds inmost sections to be correlated. This correlation provides the basis for a series of palaeogeographic maps which suggest that in the Wenlock (unlike the Llandovery) there was a complex topography in the Welsh basin. The distribution of shallow water sediments shows that many topographic highs and lows were ephemeral; only in one instance (the Church Stretton Fault in latest Wenlock time) are the topographic features related to any known fault. In the Wenlock, there is generally no sharp edge to the shelf; the sharp edge seen in the Llandovery (and at the present time) may be related to the changes in sea level associated with polar ice caps. During the Wenlock, much of England was covered by sea, and the clastic sediments of the Welsh basin were derived from the Irish Sea landmass and perhaps from a land area in the East Midlands.

Studies in the sedimentation of the Lower Greensand of the Weald, 1875–1975: a review and commentary

A review is given of developments in six fields of sedimentological studies during the last century: heavy mineral studies, mechanical analysis, cross-bedding studies and investigation of the formation of chert, of fuller's earth and of the processes of cementation and decalcification. Theories of the provenance of the Lower Greensand sediments are discussed. In conclusion the palaeogeography of Lower Greensand times, as suggested by sedimentological studies, is discussed and illustrated by means of a palaeogeographic map.

Vertebrate Palaeodistributional Patterns and Continental Drift

The patterns of distribution of vertebrates (primarily terrestrial forms) are analysed from the Silurian onwards, using palaeogeographical maps which show epicontinental seas as well as intercontinental oceans. Silurian vertebrates (fish) are known almost exclusively from Euramerica. Many Devonian fish which are normally found in fresh waters seem to have been able to cross intervening seas between one continent and another. It is suggested that this ability may be physiologically related to their capacity to use aerial respiration. There is some evidence for a separate Devonian osteostracan fish fauna in China. Amphibians are first known from the uppermost Devonian of the Euramerican continent, and land vertebrates are known almost exclusively from that continent until the Mid Permian. It is suggested that tetrapods may have evolved in Euramerica, and were only able to colonize Asia and Gondwanaland after continental drift had linked these areas with Euramerica, causing the Uralian and Alleghanian orogenies.

Facies relationships in the Upper Devonian‐Lower Carboniferous of southwest Ireland and adjacent regions

AbstractIn southwest Ireland 2,500 m of Upper Famennian to basal Namurian marine sandstones and mudstones, the Cork Beds, overlie rocks of Old Red Sandstone facies. Coastal exposures of the Cork Beds are interpreted as showing gradual upward change from alluvial strata, through thick subtidal and shelf sediments to pyritic muds. A review of recent palaeontological evidence shows that the thick shallow marine part of the Cork Beds is older than the major development of lime‐stones north of the Cork Harbour—Kenmare Une, whose equivalents to the south are in the condensed basinal sediments. The Lower Carboniferous portion of the Cork Facies is shown to be thicker in South Cork than in West Cork. In Lower Carboniferous times a positive area–the Glandore High–separated two sub‐basins with different depositional histories. Six palaeogeographic maps are used to demonstrate the progressive shift of facies belts as Lower Carboniferous marine transgression progressed. Finally, brief comparison is made with rocks of the same age in southwest England.

Palaeogeographical significance of some aspects of Palaeogene and Early Neogene stratigraphy and tectonics of the Timor Sea region

New evidence from Timor and the Ashmore Reef offshore well suggest that the Palaeogene and Early Neogene geological history of Timor was very different from that of the Sahul Shelf and northern Australia. Recently published correlations between Timor, Ashmore Reef and Australia are disputed and another solution is proposed. Lower Miocene limestones, whose status is critical to the understanding of Timor's Cenozoic tectonic and stratigraphical history, are shown by unambigous field evidence to be autochthonous. This allows a pre-Miocene major orogenic phase in Timor to be confirmed. On the basis of new stratigraphical evidence a mechanism is proposed to explain the development of the Lower Miocene autochthonous “fatus”, which relates their origin partly to lateral facies changes in the Lower Miocene and partly to their subsequent mode of erosion by the emplacement of the Bobonaro olistostrome. New evidence is given in support of an earlier contention, recently challenged by Veevers (1969), that a Timor trough separating the Sahul Shelf from Timor has existed since the Early Eocene. Utilising recent information from a deep offshore well at Ashmore Reef and recently published drift rates for the Indian Ocean-Australian plate and palaeomagnetic laeolatitudes for Australia a series of palaeogeographical maps for the Timor Sea region have been drawn.