Faunal Migration Research Articles

Possible influence of Gondwanan glaciation on low-latitude carbonate sedimentation and trans-equatorial faunal migration: the Lower Permian of South China

Peculiar Early Permian palaeontological and sedimentological features are reviewed from South China, including characteristic Early Permian cold-water Gondwanan brachiopod taxa and faunas from Sichuan and Guizhou provinces, widespread rosettes and irregular aggregates of calcite prisms ('Chrysanthemum Stones') within the Qixia limestones, and lack of significant Early Permian reef buildups. The occurrences of these features are at odds with the currently widely held view that South China was located in a palaeotropical, warm-water setting throughout the Permian and hence harboured a highly diverse shallow marine biota. In this paper, I propose a working hypothesis, suggesting that influence of at least cool water masses may have intermittently occurred in South China during the Early Permian, which facilitated the formation of the cool water-influenced palaeontological and sedimentological features and promoted the interchanges of cool to cold water marine faunas between the Gondwanan and Boreal Realms. These cool water masses may have been transported to low-latitude regions as deep currents from northern and eastern shelves of Gondwanaland and upwelled along the western coast of South China as well as within the relatively deep-water basins of central South China. Prevalence of these meridional, north-directed deep cold water currents during the Early Permian may have been related to the glaciation event of Gondwanaland. An alternative and/or additional source of cooling may have also originated from strong easterly palaeoequatorial boundary currents operating within the Palaeotethys at times during the Early Permian, inducing and/or enhancing upwelling of cool to cold water masses in the eastern Palaeotethys. This latter scenario is analogous to the occasional 'La Nina' effect (opposite to the 'El Nino' effect) at the equatorial belt of the modern Pacific Ocean.

High concentrations of greenhouse gases and polar stratospheric clouds: A possible solution to high-latitude faunal migration at the latest Paleocene thermal maximum

High concentrations of greenhouse gases and polar stratospheric clouds: A possible solution to high-latitude faunal migration at the latest Paleocene thermal maximum

High concentrations of greenhouse gases and polar stratospheric clouds: A possible solution to high-latitude faunal migration at the latest Paleocene thermal maximum

High-latitude faunal migrations have been documented during a rapid warming event near the Paleocene-Eocene boundary (the latest Paleocene thermal maximum, LPTM). The migrations are difficult to explain from a climate perspective. Climate along these routes is at present too harsh to support the migrations, and no mechanism has yet proved adequate to explain the past high-latitude warmth required by such migrations. A large negative excursion in the δ13C record at the LPTM suggests that a large quantity of CH4 was released into the atmosphere at this time. High concentrations of atmospheric CH4 have been linked to the formation of polar stratospheric clouds. We used an atmospheric general circulation model to explore early Cenozoic climate response to the combined effects of high atmospheric CH4 levels and polar stratospheric clouds, a unique combination of forcing factors in paleoclimate modeling studies. Our interests are in understanding if the climate response to this forcing may explain the high-latitude faunal migrations. Model results indicate that high-latitude winter warming with high methane levels and polar stratospheric clouds is sufficient to facilitate the high-latitude migrations. Temperatures along high-latitude migration routes remained above freezing year-round and thus permitted exchanges of fauna between Asia, North America, and Europe. On the basis of our results, we suggest that other Paleogene migrations may be correlated with LPTM-like events with high concentrations of greenhouse gases and polar stratospheric clouds.

Late Cretaceous and Cainozoic bathyal Ostracoda from the Central Pacific (DSDP Site 463)

Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct faunal assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some faunal exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively.

Early Cretaceous ammonoid paleobiogeography of the West Carpathian part of the Paleoeuropean shelf margin

The diversity and distribution of ammonites in the Tithonian and Lower Cretaceous of the Western Carpathians reflects local paleogeography. Ammonites were more diversified on the European shelf from the Tithonian to the Valanginian, despite the preservational bias in the Central Carpathian sequences. This area was intermittently connected to the Boreal Realm by seaways, through which faunal migrations took place. By contrast, ammonite assemblages (purely Tethyan) of the Zliechov Basin on the Alpine Carpathian microplate displayed maximum diversity in the Hauterivian. The most diverse Barremian and Aptian ammonite associations are found in the Godula Basin. Albian ammonites were relatively rare and only known from the borders of the Penninic Oceanic Trough.

The stratigraphic distribution of graptolites in the classic upper Middle Ordovician Utica Shale of New York State: an evolutionary succession or a response to relative sea-level change?

The stratigraphic distribution of graptoloid species within the upper Middle Ordovician strata of New York State represents a complex pattern of origination, extinction, faunal migration, and fluctuating relative abundances. In particular, the observed patterns of species turnover at graptolite biozone boundaries are apparently strongly correlated with lithofacies, sampling strategies, and the depositional effects of relative sea-level change.Vertical facies changes that occur within third-order depositional sequences and fourth- or fifth-order parasequences are mirrored by changes in the graptoloid faunal composition. Large-scale faunal turnovers at biozone boundaries tend to occur either at sequence boundaries or at flooding surfaces within sequences (e.g., the base of Highstand System Tracts). The base of theCorynoides americanusandClimacograptus (D.) spiniferusZones coincide with major onlap events, and theOrthograptus ruedemanniZone fauna appears just below a Lowstand Systems Tract. Within individual biozones, smaller-scale changes such as the fluctuating relative abundances of graptoloid species coincide with higher-order parasequence cyclicity. These distribution patterns resemble recent computer-generated models for the sequence stratigraphic distribution of hypothetical taxa.By combining good biogeographic control with a detailed sampling program, we are able to see through the patterns attributable to depositional cyclicity and identify the different components of faunal turnover (migration, speciation, and extinction).

Biogeography of Ordovician sponges

Sponges have an unrealized potential importance in biogeographic analysis. Biogeographic patterns determined from our analysis of all published data on distribution of Ordovician genera indicate Early Ordovician sponge faunas have relatively low diversity and are completely dominated by demosponges. Early Ordovician (Ibexian) faunas are characterized by the widespread co-occurrence ofArchaeoscyphiaand the problematicCalathium.This association is commonly found in biohermal structures. Middle Ordovician faunas show an increase in diversity, and two broad associations are differentiated: Appalachian faunas (including Southern China and the Argentine Precordillera) and Great Basin faunas.Late Ordovician faunas show important changes in diversity and provincialism. Hexactinellid and calcareous sponges became important and new demosponge families appeared. Four Mohawkian-Cincinnatian associations are recognized here, including: 1) Midcontinent faunas; 2) Baltic faunas; 3) New South Wales faunas; and 4) Western North American (California and Alaska) faunas. However, two separate biogeographic associations are differentiated based on faunal differences. These are a Pacific association (western North American and New South Wales) and an Atlantic association (Midcontinent Laurentia and Baltica).Distribution of sponge genera and migration patterns are utilized to consider paleogeographic dispositions of the different continental plates, climatic features, and oceanic currents. Such an analysis points to close paleogeographic affinities between the Argentine Precordillera and Laurentian Appalachian faunas. However, significant endemicity and the occurrence of extra-Laurentian genera suggest a relative isolation of the Precordillera terrane during the Late Ibexian-Whiterockian. The study also shows a faunal migration from the Appalachian region to South China during the Middle Ordovician and the migration of faunas from Baltica to Laurentia in the Late Ordovician. The occurrence of Laurentian migrants in New South Wales during the Late Ordovician could be related to inferred oceanic current circulation between these two areas, although other paleogeographic features may be involved.

A new mosasaur Pluridens walkeri from the Upper Cretaceous, Maastrichtian of the Iullemmeden Basin, southwest Niger

ABSTRACT A new mosasaur from the Iullemmeden Basin in S.W. Niger, Pluridens walken gen. et sp. nov., has a highly anteriorly elongated dentary with at least one and a half times the number of teeth of any other recorded mosasaur. Referred material of P. walkeri is also recorded from southern Nigeria, providing vertebrate evidence that a seaway connected the Iullemmeden Basin to the Gulf of Guinea in the south and to the Tethys in the north, i.e., that the seaway was apparently open-ended. The ecology and evolution of mosasaurs from west and southwest Africa are discussed in relation to a Trans-Saharan Seaway and faunal migrations. Mosasaurs in the Iullemmeden Basin appear to have been adapted to a shallow sea and lagoonal environment. A new feeding strategy is proposed for mosasaurs i.e., it is possible that Pluridens walkeri occupied the vacated feeding niches of the early ichthyosaurs.

Hydrothermal activity along the southwest Indian ridge

Twenty years after the discovery of sea-floor hot springs, vast stretches of the global mid-ocean-ridge system remain unexplored for hydrothermal venting. The southwest Indian ridge is a particularly intriguing region, as it is both the slowest-spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans2. A recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity2. Here, however, we report evidence of hydrothermal plumes at six locations within two 200-km-long sections of the southwest Indian ridge indicating a higher frequency of venting than expected. These results suggest that fluxes of heat and chemicals from slow-spreading ridges may be greater than previously thought and that faunal migration along the southwest Indian ridge may serve as an important corridor for gene-flow between Pacific and Atlantic hydrothermal fields.

Terminal Cretaceous warming event in the mid-latitude South Atlantic Ocean: evidence from poleward migration of Contusotruncana contusa (planktonic foraminifera) morphotypes

Abstract Spatial and temporal patterns in test size and shape (test conicity and spiral roundness) and absolute abundance (accumulation rate) of the planktonic foraminifer Contusotruncana contusa were studied in the South Atlantic Ocean (DSDP sites 356, 516, 525 and 527) during an interval corresponding to the last 800 kyr of the Cretaceous. The variation in absolute abundance of C. contusa was characterised by alternating periods of high and low abundance; some of these periods were traceable across the entire mid-latitude South Atlantic Ocean. While the mean spiral roundness did not show any interpretable patterns, a sudden increase of the mean test size and mean test conicity occurred between 65.3 and 65.2 Ma (based on linear interpolation within the Cretaceous part of Subchron C29R) at all sites studied, indicating a poleward migration followed by rapid withdrawal of the low-latitude C. contusa morphotypes from the mid-latitude South Atlantic Ocean. We suggest that this event was caused by a short period of surface-water warming in the southern mid-latitudes corresponding to the brief high-latitude warming event and associated faunal migrations in the Boreal and Austral realms.

Thermally anomalous assemblages revisited: Patterns in the extraprovincial latitudinal range shifts of Pleistocene marine mollusks

Pleistocene faunas of the eastern Pacific shelf are characterized by thermally anomalous species assemblages—i.e., coexisting species that inhabit different climatic regimes today. We used data on the latitudinal ranges of 2887 extant molluscan species to determine the biological basis of the Pleistocene faunal migrations. Overall, the species exhibiting the most extensive range shifts (termedextraprovincialspecies)werenotdrawnrandomlyfromthe availablespeciespool,andthepatternisclimaticallyasymmetrical. The latitudinal ranges of southern extraprovincial species are significantly wider on average than those of the species pool from whichtheyweredrawn,buttherangesofnorthernextraprovincials resemble those of their parent pool. This contrast is primarily a consequence of the biogeographic structure of the eastern Pacific fauna;water-massboundariesaremoreeffectivebarriersforsouthern species migrating north in response to changing climatic conditions than for northern species moving south. Our analysis of Pleistocenemarinemollusksprovidesabiologicalandenvironmental context for species response to environmental change and permits predictions about the movement of eastern Pacific species relative to major environmental barriers in the face of future global change.

Palaxius caucaensis n. sp., a Crustacean Microcoprolite from the Basal Nogales Formation (Campanian to Maastrichtian) of Colombia

From a sandstone layer of the basal Nogales Formation (Campanian to Maastrichtian) of Colombia (South America) the new crustacean microcoprolite Palaxius caucaensis is described. It represents the first finding of these microfossils in Cretaceous beds in South America. INTRODUCTION Until now crustacean microcoprolites from South America have been known only from Triassic and Jurassic sediments (Forster and Hillebrandt 1984, Senowbari-Daryan and Stanley 1986, Blau et al. 1993, Blau and Senff 1993). Whereever these coprolites occur, they are often the only fossil group preserved and therefore of great stratigraphical interest. The value of crustacean microcoprolites for biostratigraphy has been demonstrated by Molinari Paganelli et al. (1980, 1986). Additionally, crustacean microcoprolites are a good tool for paleobiogeography and the reconstruction of faunal migration paths (e.g., Blau et al. 1993). In this paper, we describe the first Cretaceous crustacean microcoprolite from South America. ORIGIN OF THE SAMPLE The investigated outcrop is situated SE of Monteloro (Departamento Valle del Cauca) at the western flank of the Central Cordillera of Colombia on sheet 261 Tulua. Close to the locality known as El Paraiso, about 200m of shallow marine conglomerates, sandstones and claystones crop out in a nameless eastern confluent of the Quebrada (creek) La Mina (text-fig. 1). The sample which yields the coprolites originates from a sandstone layer near the base of the profile. The Nogales Formation The Nogales Formation crops out in a narrow north-south directed strip along the western flank of the Central Cordillera of Colombia, southeast of the city of Tulua. It is limited to the west by a fault against rocks of the Amaime Formation and the batolith of Buga, while to the east the Nogales Formation disappears under the tertiary cover. It was described first by Nelson (1957) as a unit consisting of black cherts and grey sandstones. Pardo et al. (1993) subdivided the Nogales Formation into three units. The lower part contains (graded) sandstones and matrix-supported conglomerates which sometimes have an important content of carbonate. The conglomerates are composed of metamorphic, volcanic and sedimentary rock fragments and show diameters up to 10cm. The middle part of the Nogales Formation shows an alternation of sandstones and claystones with some intercalated chert layers. Slumping structures are frequent. The upper part is dominated by claystones and cross-bedded, fine-grained sandstones. Especially in the lower part, the Nogales Formation yields plant remains, internal molds of bivalves, gastropods and ammonites. F. Etayo-Serna (Bogota) kindly determined Trochoceramus sp. and Nostoceras sp., which indicate a Late Cretaceous (Campanian to Maastrichtian) age for the lower part of the Nogales Formation which also contains the finding horizon of the coprolite-bearing sandstone layer. In the upper part of the Nogales Formation van der Hammen (1960) found a sporal assemblage of Paleocene age. According to these data, the Nogales Formation is the youngest marine sedimentary unit at the western flank of the Colombian Central Cordillera. SYSTEMATIC PALEONTOLOGY Phylum ARTHROPODA Subclass MALACOSTRACA Superorder EUCARIDA Order DECAPODA Family THALASSINIDAE Genus Palaxius Bronnimann and Norton 1960 The genus Palaxius was defined by Bronnimann and Norton (1960) as having crescent shaped canals in cross-sections. Recently, Blau et al. (1994) have demonstrated that crescent-shaped canals also oc ur together with triangle-shaped canals in Parafavreina thor netensis Bronnimann et al. 1972a. Palaxi s caucaensis Blau, Moreno and Senff n. sp. Text-figures 2a-e, 3a-d Etymology: Named after the Valle del Cauca, where the coprolites were found. Holotype: The specimen illustrated in text-fig. 2c, thin section no. M-12, tored at the Institut fur Angewandte Geowissenschaften, Fachgebiet Palaontologie, Justus-Liebig-Universitat, Diezstrasse 15, D-35390 Giessen. Type locality: Nameless eastern confluent of the Quebrada La Mina (text-fig. 1). micropaleontology, vol. 41, no. 1, pp. 85-88, text-figures 1-5, 1995 85 This content downloaded from 157.55.39.159 on Fri, 09 Dec 2016 05:24:19 UTC All use subject to http://about.jstor.org/terms Joachim Blau et al.: Palaxius caucaensis n. sp., a crustacean microcoprolite from the basal Nogales Formation of Colombia

Genetic types of manganese oxide deposits in Scotland; indicators of paleo-ocean-spreading rate and a Devonian geochemical mobility boundary

There are over 70 occurrences of manganese oxides throughout Scotland; of these, only 13 are sufficiently well developed to be worthy of description. The deposits are categorized on the basis of the formation processes; eight are supergene ground-water or soil deposits, three formed by weathering, and two are hydrothermal in origin. The chemistry of marine sedimentary exhalative deposits can be related to the paleospreading rate of the once-active ridge and, under favorable conditions of stratigraphic preservation, be used to estimate the halfwidth of the ancient ocean. This approach yields estimates of 5 cm yr (super -1) and about 1,000 km for the spreading rate and maximum half-width of the Ordovician Iapetus ocean, respectively: figures which compare favorably with earlier estimates from faunal migration studies.Several of the Scottish manganese outcrops are associated with Old Red Sandstone (Devonian) sediments--a continental fluvial-lacustrine facies in northern Scotland. Diagenetic remobilization, with subsequent oxidation and deposition, of the manganese within the lacustrine sediments led to the formation of a manganese-rich horizon in the uppermost sections of the Old Red Sandstone sedimentary pile. Previously immobile in the pre-Devonian inorganic reaction-dominant regime, manganese mobility increased dramatically with the introduction of large quantities of organic acids following terrestrial colonization by plants. Climate change from arid to tropical with increased vegetation development promoted the formation of thick, organic-rich soils with the concomitant increase in available manganese-chelating ligands. Organomanganese reactions fundamentally changed the pattern of manganese mobility in the postcolonization surficial environment, making the Devonian a stratigraphic geochemical boundary. These changes in weathering processes would also affect the dispersal patterns of other metals which form organo complexes, gold being an obvious example.

Late Ordovician extinctions of bryozoans

An analysis of the final stratigraphic appearances of byrozoan species and genera, compiled in a world-wide bryozoan data base, revealed three discrete Late Ordovician extinctions. A Late Carddoc (Onnian) extinction was most pronounced on the plates of Baltica and Siberia. Endemic species and genera, confined to one plate and one lithotope were most affected and the extinction was coincident with increased migrations of bryozoan genera to Baltica and Siberia. The Late Caradoc extinction may be related to decreasing provinciality and competition between migrant and stenotopic taxa. Two major extinctions occurred in the Late Ashgill. The greatest of the two is recognized at the end of the Rawtheyan. and affected primarily taxa on the North American plate. The extinction at the end of the Hirnantian affected primarily Baltic taxa. The exact timing of the end-Rawtheyan extinction in North America cannot be established owing to incompleteness of the stratigraphic record. The Rawtheyan extinction occurred during a major glaciation centered in North Africa and a regression of epeiric seas. The large majority of North American survivors of the extinction are represented by Faunas preserved on Anticosti Island. which remained submerged during the regression. This evidence supports regression as a cause of the Rawtheyan extinctions in North America. The end-Hirnantian extinctions may be related to the ensuing transgression or to a wave of faunal migrations associated with the transgression. *Bryozoa, extinctions, Ordovician, Rawtheyan, Hirnantian, North America, Baltica.

Jurassic and cretaceous marine connections between the Southeast Pacific and Tethys

The affinities of the ammonoid faunas from central-west and southern South America are used to analyze the evolution of seaways and oceanic connections with Tethys during the Jurassic and Cretaceous. During the Early and Middle Jurassic, marine connection with eastern Tethys was around the Australian margin of Gondwana. From the Pliensbachian onwards, connection with western Tethys occurred through the sporadically opened “Hispanic Corridor” in Central America. In Late Jurassic time, the break-up of Gondwanaland was initiated and a seaway began to open between South America-Africa and Antarctica. Connection of the eastern Pacific with Tethyan waters through southern Africa was sporadic and was still mainly around Australia and along the now open Central American seaway. Throughout the Early Cretaceous, the opening of the South Atlantic proceeded from south to north, and the first marine connection between the southern and northern Atlantic took place in Albian time. A definite marine connection between the opened South Atlantic and eastern Tethys, with faunal migration routes, was established in Late Hauterivian-Barremian time and became fully open in the Aptian-Albian. Successive stages in the opening of a South African seaway between Tethys and the southeast Pacific show an asymmetric development to the west and east of South Africa. During Late Cretaceous time oceanic circulation continued between the South Atlantic and eastern Tethys, and true oceanic conditions developed between the southern and northern Atlantic. The Antarctic Peninsula was still located in a position adjacent to South America, preventing open circulation between the South Atlantic and Pacific oceans.

Ordovician sedimentary facies and faunas of southwest Europe: palaeogeographic and tectonic implications

Abstract The term st European Platform is introduced for an Ordovician shelf now within the western Variscides. The geometry of the sedimentary facies belts and their faunal variation suggest that it formed a promontory on the Gondwanan margin. The palaeogeography of the platform is discussed with particular reference to the Centro-Iberian/Armorican area, especially central Portugal. The sedimentary history of the Centro-Iberian/Armorican area was controlled by basement structures. Rapid local subsidence during Early Ordovician extension was followed by later differential subsidence along these early structures. The thin sequences indicate low overall rates of subsidence. The dominantly clastic shallow marine sediments show strong storm influence. Individual sediment packets occur over wide areas indicating little syndepositional relief. The linear nature of facies belts allows reconstruction of the relative orientation of some blocks within the Variscides, and indicates strike-slip faulting during early Variscan events, with subsequent (Carboniferous) rotation of most of Iberia. Faunas from SW Europe from a homogeneous group related to those of the classic 'Mediterranean Province' areas of Bohemia and Morocco, and more distantly to those of the Avalonian terrane. Faunal migration into the West European Platform from Avalonia accompanied progressive northward drift of the platform, occuring particularly during periods of eustatic sea-level rise in the early Llanvirn, the early Caradoc and the early Ashgill

Diversification and extinction patterns among Neogene perimediterranean mammals.

The best mammalian fossil record during the Neogene of Western Europe is that of the rodents, the most successful and diversified mammal order. The study of origination and extinction during the Neogene (24-3 Ma BP) in one of the best-documented areas, Spain and southern France, gives an insight into the dynamics of these communities and indicates the possible nature of the driving forces. Three main periods of time show a high rate of origination: the late Burdigalian (17.5 Ma BP), the early Vallesian (11.5-11 Ma BP) and the early Pliocene (4.2-3.8 Ma BP). Two of these high origination-rate periods are immediately followed by important extinction events during which all cohorts are deeply affected (11.5-11 Ma BP and 4.2-3.8 Ma BP). The most important extinction event seems to occur during the early Vallesian (11.5-11 Ma BP), which probably includes the middle/late Miocene boundary. At the Miocene/Pliocene boundary, and during the early Pliocene, the faunal turnover seems to become faster, inducing a strong decrease of the mean species duration. Whereas the main immigration event, which occurs at 17.5 Ma BP, can be related to other faunal migrations in terms of the closure of the Tethys, as it occurs also in eastern Africa and in southwest Asia, the middle/late Miocene boundary event may have been related to a period of ice growth in the Southern Hemisphere. The extinction event that affects the planktonic foraminifera at 12 Ma BP cannot be chronologically correlated to this southwestern European land-mammal extinction event, because the calibration of the marine fossil record during that time-span has to be precise. Some limited terrestrial faunal exchanges that occur during the Messinian between southwestern Europe and northwestern Africa do not deeply affect the general faunal dynamics. Both allochthonous cohorts of immigrants become rapidly extinct. Several endemic rodent faunas, indicating insular conditions, have been reported from the southern edge of the western European continent from the middle Miocene up to the Pliocene. All show low taxonomic diversity, strong endemism and short survival. Some of them, like those of the Gargano Islands during the late Miocene, underwent peculiar morphological changes and also speciation. The large number of rodent genera coevolving in the Gargano Islands is indicative of the large surface areas of these islands. The general geographic pattern of southwestern Europe during the Neogene may therefore correspond to a large continental province including Spain and southern France with some kind of fast-modifying archipelago on its southern rim.

Variations in high‐latitude oceanographic fronts in the southern Indian Ocean: An estimation based on faunal changes

A quantitative estimate of the magnitude of late Pleistocene/Holocene variations in the migration of siliceous microfauna is calculated from fossil assemblages preserved in marine sediments from piston cores located in the southeast Indian Ocean sector of the Subantarctic. Results of this modern analog technique indicate that fauna characteristic of colder waters today occupied surface and near‐surface waters overlying the core sites for much of the last half million years. Warm‐water fauna inhabited these waters for only brief time periods, usually during the early portion of interglacial isotopic stages. The estimated faunal migration pattern from the most southern sites is similar in most respects to that of atmospheric temperatures over Antarctica recorded in the Vostok ice core. A model of changes in the positions of the Subtropical Convergence and the Antarctic Polar Front, constructed from time series of faunal variations, indicates that although southward migrations of these oceanographic fronts in this region of the southern ocean were limited to approximately 4° of latitude, northward displacements were of the order of 5° to 7° of latitude. Fauna at the Antarctic Polar Front react earlier than either the fauna at the Subtropical Convergence or the global ice volume signal to major global warming (terminations), providing further documentation of the early response of the high‐latitude southern ocean relative to other components of the climate system to the various factors forcing Pleistocene climate.

Polar glaciers and life at the equator: The history of Dinantian and Namurian (Carboinferous) climate

Biotic migration patterns provide a history of relative climate change that can be used to study Dinantian and Namurian (Carboniferous) climates. High-latitude warming between the middle and late Visean may have been caused by the collision of Laurussia and Gondwana. High-latitude cooling and equatorial warming between the Namurian A and B may have been caused by the onset of glaciation in the Southern Hemisphere. Patterns of faunal migration and extinction and floral radiation were similar during Namurian and Miocene glacial onsets, and provide criteria for assessing other extinction events tied to changes in paleoclimate.

Répartition des dépôts carbonatés du Lias inférieur et moyen le long de la côte atlantique du Maroc: conséquences sur la paléogéographie de l'Atlantique naissant

Along the Atlantic coast of Morocco a series of embayments or basins including the Essaouira-Jebel Amsittène and Tarfaya-Laayoune basins, contain marine sediments which may attain considerable thickness and whose Early Jurassic (Liassic) age has been well documented. This paper describes Liassic deposits from six exposures or drill holes between the Saharan coast of Tarfaya and the Essaouira-Jebel Amsittène region. These Atlantic basins do not connect with the marine troughs of the High and Middle Atlas, which follow a Mediterranean Tethys trend, but are separated from them by a SSW-NNE trending threshold made up of the axial portion of the central Hercynian Massif (Moroccan Meseta). Their opening to the ancestral Mediterranean must have been farther north, probably by means of interconnecting, WSW-ENE trending rift-related graben trenches, possibly starting with the Rharb (Kenitra) basin. More likely, however, openingsexisted beneath the present nappes of the Rif and along the undoubtedly wide fracture zone represented by the Azores-Gibraltar line separating the Rif terrain from that of the Betic Cordilleras (both of which contain well dated marine Hettangian). Farther SW, probably hidden by the sedimentary prism of the African continental shelf, connections may exist with the Liassic occurrence of Central America, as already suggested by Avias (1953. Sci. Terre 1 (1), 1–276; 1956. 20° Congr. géol. Intern Mexico, Secc. II, 1–5), shown in a figure by Erben (1956b. Neues Jb. geol. paläontol. Abh., Stuttgart 103, 28–79), and subsequently upheld by Hallam (1971a. J. Geol. Chicago 79 (2), 129–157; 1983. Palaeogeogr. P. clim. P. ecol. 43, 181–193) and Thierry (1982. Bull. Soc. géol. Fr., Sér. 7, 24, 1053–1067). These lines of communication would have centered on a “Panamanian Strait” (“Panama Strasse”) and would have permitted faunal migrations, in particular towards South America. Migrations of certain European and Mesogean faunal species have recently been proposed by Schmidt-Effing (1976a. Münster Forsch. Géol. Paläont. 38–39, 201–217; 1976b. Publ. geol. ICAITI, Guatemala, 5, 22–23; 1980. In: The Origin of the Gulf of Mexico and the Early Opening of the Central North Atlantic Ocean (Edited by Pilger, R. H., Jr), pp. 79–86, Von Hillebrandt (1981b. Geol. Rdsch. 70 (2), 570–582; 1984. Int. Symp. Jurassic Stratigraphy 3, 716–729) and Riccardi (1983. In: The Phanerozoic Geology of the World (Edited by Moullade, M. and Nairn, A. E. M.), II. B, 201–264). Unless one believes that in all localities cosmopolitan faunas arrived from a universal ocean, these relationships lead to the model of an “Atlantic corridor”, starting in the Middle, and perhaps even the Early Liassic (the “Paleotethys” of Bernoulli and Lemoine, 1980. Mém. Bur. Rech. géol. min. 115, 168–179; or the “proto-Atlantic” or “Atlantic Tethys” of Lancelot, 1980. Mém. Bur. Rech. géol. min. 115, 215–223; and Lancelot and Winterer, 1980 Initial Report of the Deep Sea Drilling Project 50, 801–821; although the latter authors postulate such a connection only from Late Liassic time on). This model raises the specific question whether or not Early Jurassic deposits are present in the Senegal basin (Guieu, 1976. Rapp. Dépt. Géol. Fac. Sci. Univ. Dakar 32, 1–87).