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Paleogeography of North America

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... Multi-taxon global bioregionalisations have been the backbone of both biogeographic (Sclater 1858;Wallace 1876) and palaeobiogeographic studies (Arldt 1907;Schuchert, 1909). The descriptions of areas and their nomenclature (sensu Wallace 1894; Arldt 1912) have been vital to maintaining existing bioregionalisations, reducing the number of conflicting terms and descriptions. ...
... basins, formations, assemblages), or the continents themselves (e.g. North America, Gondwana, Lemuria, Archiplata; see Suess, 1885;von Ihering, 1892;Schuchert, 1903Schuchert, , 1909. ...
Article
We present an interim Devonian bioregionalisation in which previous zoogeographical and biogeographical areas of Devonian taxa are reviewed. This review has been long overdue, as Devonian bioregionalisation has become poorly constrained since the foundational work of Arthur J. Boucot in the late 1960s. A systematic review of over 100 areas and amendments is completed for the first time with addition of three new areas: the Mardoowarra and the Late Devonian Eastern Australasia region, and Western Gondwana realm. This interim regionalisation is the first to be completed and standardised, made in preparation for future palaeobiogeographic studies and as a prelude to rigorous testing. By standardising the 1969 bioregionalisation of Boucot et al. Devonian biogeography can begin to assess if the proposed bioregionalisation is representative of true natural areas.
... In this review, Arldt considers palaeogeography to extend to biogeographic studies that attempt to map biotic distributions across continents, regardless of whether this is done cartographically or descriptively. Compare this to earlier historical reviews by US geologist Charles Schuchert (Schuchert 1910) and Dacqué (1915), in which the discussion is largely confined to the geological and palaeontological literature. Arldt was clearly inspired by Wallace in that he included biogeography, and in turn biology (e.g., taxonomy, phylogenetics), into the remit of palaeogeography which he coined 'palaeobiogeography' (Arldt 1909). ...
... Only a few historians mention Arldt, but generally in connection to Wegener and continental drift rather than to palaeogeography and palaeobiogeography (e.g., Frankel 2012;Greene 2015;Hofsten 1916;Wagenbreth 2014;Le Grande 1988 with no formal education (Oreskes 1999). By 1904, at the age of 46, Schuchert was a Professor at Yale and in 1910 came to international attention with his famous Paleogeography of North America (Schuchert 1910). The work, written while he was a Professor at Yale, launched his career as a "noted palaeontologist and foremost palaeogeographers of our times" (Dunbar 1943, p. 301). ...
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The rise and fall of Theodor Karl Hermann Arldt (1878–1960) took place in Radeberg, a small town in Saxony between 1902 and 1945, where he supported his research by working as a school headmaster or Pauker. Within his many scientific papers and books Arldt pioneered palaeogeography and palaeobiogeography by introducing distributional data of living organisms to understand past continental connections. His writings influenced notable scientists such as Alfred Wegener and partially influenced the geological community in which palaeogeography was firmly rooted. While Arldt’s biogeographic approach was novel, and in hindsight surprisingly modern, it failed to engage biologists where such a method may have flourished. As a small town Pauker, Arldt had little or no contact with universities and university students, leaving a legacy of pioneering publications and ideas but no one to carry them forward into the post-tectonic world of the 1960s.
... Geologists have been mapping the changing extent of land and sea for more than 200 years (Smith, 1815). One of the earliest works, Schuchert's (1910Schuchert's ( , 1955 atlas the "Paleogeography of North America", was illustrated by 50 maps describing the flooding of North America by vast epeiric seas from the Cambrian to the Pliocene. State-of-the-art paleogeographic (paleocoastline) reconstructions follow and incorporate key sources, including the work of Bozhko and Khain, 1987;Cook (1990); Cook and Bally, 1975;Cope et al. (1992); (Dercourt et al., 1985(Dercourt et al., , 1993(Dercourt et al., , 2000; Golonka (2000); Kazmin and Natapov (1998); Mallory (1972); McCrossan et al. (1964); (Ronov et al., 1984(Ronov et al., , 1989; Scotese (2004Scotese ( , 2009); Scotese, 2016); Scotese et al., (1979), Scotese and Wright (2018) ;Stampfli, (2000); Stampfli and Borel, (2002) ;Veevers, 1984Veevers, , 2000Vinogradov et al. (1967Vinogradov et al. ( , 1968aVinogradov et al. ( , 1968bVinogradov et al. ( , 1969, Wang (1985), Ziegler et al. (1977Ziegler et al. ( , 1979Ziegler et al. ( , 1983Ziegler et al. ( , 1985Ziegler et al. ( , 1997; Ziegler (1982Ziegler ( , 1988Ziegler ( , 1989Ziegler ( , 1990; Zonenshain et al. (1990). ...
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Sea levels shape the face of the Earth, define processes of sedimentation, and influences the evolution of life via the distribution of habitats. Ancient topographies can be reconstructed using the history and understanding of tectonic processes, lithological evidence, and present-day topographies. Paleogeographic reconstructions must accommodate ever newer sources of geological data, so we can refine and improve our model of ancient topography and bathymetry. Here, we assess the accuracy of a Phanerozoic set of digital paleogeographic maps by testing the proposed distribution of flooded shallow seas and land using fossil occurrence data from the Paleobiology Database. After noting a moderate match, we modified the positions of the coastlines and continental margins of these topographic models to reflect times of maximum transgression. Using the updated paleogeographic maps, we outline the changes of land and shallow marine areas over time and suggest ways they can be used for further investigations of our planet's history.
... Studies of mountain belts, and the extent to which they are dynamic rather than static systems, led to an interest in tectonic processes. The recognition of similar fossils groups on different continents, and the geographic fit of some continents with continents nearby, encouraged models of lateral movement and discussion of continental drift (Schuchert, 1909;Wegner, 1912;Holmes, 1925;du Toit, 1937) before the recognition of a viable driving mechanism in the 1960s. This relied in part on studies of the ocean crust, and the recognition of "magnetic stripes" of alternating remnant magnetization in rocks symmetric to mid-ocean ridge axes (Hess, 1962;Vine and Matthews, 1963). ...
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The Earth is the only known planet where plate tectonics is active, and different studies have concluded that plate tectonics commenced at times from the early Hadean to 700 Ma. Many arguments rely on proxies established on recent examples, such as paired metamorphic belts and magma geochemistry, and it can be difficult to establish the significance of such proxies in a hotter, older Earth. There is the question of scale, and how the results of different case studies are put in a wider global context. We explore approaches that indicate when plate tectonics became the dominant global regime, in part by evaluating when the effects of plate tectonics were established globally, rather than the first sign of its existence regionally. The geological record reflects when the continental crust became rigid enough to facilitate plate tectonics, through the onset of dyke swarms and large sedimentary basins, from relatively high-pressure metamorphism and evidence for crustal thickening. Paired metamorphic belts are a feature of destructive plate margins over the last 700 Myr, but it is difficult to establish whether metamorphic events are associated spatially as well as temporally in older terrains. From 3.8 to 2.7 Ga, suites of high Th/Nb (subduction-related on the modern Earth) and low Th/Nb (non-subduction-related) magmas were generated at similar times in different locations, and there is a striking link between the geochemistry and the regional tectonic style. Archean cratons stabilized at different times in different areas from 3.1 to 2.5 Ga, and the composition of juvenile continental crust changed from mafic to more intermediate compositions. Xenon isotope data indicate that there was little recycling of volatiles before 3 Ga. Evidence for the juxtaposition of continental fragments back to ∼2.8 Ga, each with disparate histories highlights that fragments of crust were moving around laterally on the Earth. The reduction in crustal growth at ∼3 Ga is attributed to an increase in the rates at which differentiated continental crust was destroyed, and that coupled with the other changes at the end of the Archean are taken to reflect the onset of plate tectonics as the dominant global regime.
... He was one of the world's leading paleogeographers and was later referred to as the "foremost paleogeographer of our time" by the editor of a posthumous edition of one of his works (Schuchert 1955, p. iv). Schuchert had written a definitive monograph The Paleogeography of North America (Schuchert 1910). In his textbook and in many other publications, he used biogeographic principles and the idea of fixed continents to interpret the paleogeography of the world. ...
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Two papers, 'Gondwana land bridges' by Charles Schuchert and 'Isthmian links' by Bailey Willis, were published together in 1932. They were apparently motivated by Schuchert's desire to defend his paleogeography of fixed continents against the threat of Alfred Wegener's continental mobilism. Schuchert and Willis both held to land-bridge theory but admitted that they could not accept each other's types of bridges. Schuchert insisted that some bridges had to be wide and of continental material, without explaining why he felt this was so. Willis insisted that wide continental bridges were isostatically and volumetrically impossible; so any ancient bridges that had sunk must have been narrow isthmuses of dense oceanic rocks. They wrote separate papers, but issued together, perhaps to lead readers to the impression that a compromise was possible; but it was not. They avoided alerting readers to fatal flaws in both their models, in part by limiting their discussion to the less familiar southern hemisphere (Gondwana) and never mentioning the continental connection between Europe and North America. Willis went further in his inventions than Schuchert, trying to explain the extremes of Permian climate. Fixed-continent paleogeography required glacial conditions at equatorial latitudes and tropical conditions at arctic latitudes. We now understand that these climate differences can only be explained by 'continental drift' (or plate tectonics), but in his valiant effort to support fixism, Willis postulated not only tectonic uplifts of oceanic isthmuses, but also uplifts in continental areas that were known to be stable.
... Cambrian paleogeography has been an important topic since at least the time of Walcott (1892) and Schuchert (1910). Paralleling a general increase in our understanding of the Cambrian radiation, several important geologic studies have detailed late Neoproterozoic and Early Cambrian tectonic events, including the breakup of the supercontinent Rodinia. ...
Article
Important topics in Early Cambrian geology are the paleogeography of the Earth's cratons, the chronology of their separation, and evaluating the effects of tectonic events on evolutionary patterns during the Cambrian radiation. The results of an analysis of Early Cambrian biogeography are presented here to provide an independent, biological constraint on geologic and geophysical models of the breakup of some of the major elements of the supercontinent Rodinia. Biogeographic analysis is also utilized to help elucidate the relative influences of continental breakup and sea-level change on evolutionary and distributional patterns during the Cambrian radiation. This analysis suggests that rifting and continental fragmentation were the dominant processes affecting biotic evolution and distribution in the Early Cambrian; repeated episodes of sea-level rise and fall played a more limited role. Moreover, the analysis indicates that Laurentia is a well-supported biogeographic region that shares a more recent history with Siberia than with Baltica, implying that rifting between Baltica and Laurentia occurred prior to rifting between Siberia and Laurentia.
... A land bridge across the Atlantic at Iceland is shown. FromSchuchert (1910). ...
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As a geology professor teaching a course in Introductory Geology, it did not make sense to me that Alfred Wegenerʼs theory of continental drift should have been rejected for nearly half a century. From what I knew of his evidence, it seemed convincing enough. Why were geologists so against these ideas? There must have been more to this history than what was commonly known. I began this project with the feeling that the rejection of continental drift was a scandal for geology and for science. Scientists should not reject a correct interpretation for so long. In more familiar scandals, such as recent ones in finance, politics, sports, and religion, one naturally looks for cover-ups. If there were cover-ups here, what was being hidden and who was being protected? I collected all the important historical literature, and I found what I was looking for. This is a revisionist history. It is based largely on a type of historical data that has been overlooked by others – the works of leading geology textbook authors. These authors are especially important, because their textbooks teach students the principles of the science. The theory of continental drift involved a new scientific paradigm, of mobile, not fixed, continents. The textbooks used in introductory geology courses defined the fixist paradigm and influenced the likelihood of a paradigm shift. I have thus paid extra attention to what the main English-language textbook authors wrote, and tried to understand in depth how these highly respected scientists thought. I know from long experience that scientists think just the way other people do.
... He used fossils to subdivide the Jurassic of North America into 13 time intervals and produced a paleogeographic map for each interval. From this, he suggested that there was no evidence for landmasses west of the Cordilleran geosyncline to provide clastic detritus (as earlier proposed in Schuchert's (1910) borderland theory) but only volcanic archipelagos , although he allowed for tectonic lands in Triassic and Jurassic times within the geosyncline. Discussions of Cordilleran tectonics started to appear in European literature in this period. ...
Article
From the late 1800's until the 1960's, Cordilleran mountain building was viewed as the end result of geosynclinal deposition. In the 1960's geosynclinal rock units were reinterpreted in terms of their possible modern analogues and paleontological and paleomagnetic studies were used to support a mobilistic view of Cordilleran paleogeography, rather than the relatively fixed paleogeography tacitly assumed in earlier interpretations. In contrast with deterministic geosynclinal theory, it was recognized that plate-tectonic processes applied over a long time have enormous potential to create disorder; the result is an orogenic collage to be analyzed as a series of time-space events each of whose geodynamic settings may have been very different from one another. -from Author
... Palaeontologists have carried out numerous important biogeographic studies (e.g. Schuchert, 1910;Hallam, 1967Hallam, , 1977Hallam, , 1983bRowell et al., 1973;Jell, 1974;McKenna, 1975McKenna, , 1983Fortey and Cocks, 1992;Babcock, 1994; and the collected papers in McKerrow and Scotese, 1990). Thus, it is paradoxical that some biogeographers have argued that paleontology can at best be only the handmaiden of phylogenetic biogeographic studies in modern organisms (e.g. ...
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Biogeography played an important role in early developments in evolutionary theory and continues to play an important role in evolutionary studies and paleogeographic reconstructions. The development of a phylogenetic approach to biogeographic analysis has been important; however, fossil taxa have not always played a role in phylogenetic biogeographic studies and their role has been criticized by some phylogenetic biogeographers. Here, simulation studies are used to show that phylogenetic biogeographic studies on extant organisms that do not include fossil taxa can often be artificially incongruent and inaccurate. This is because area cladograms for extant taxa alone may differ from those that also include extinct taxa, implying different patterns of biogeographic relationship between areas, and area cladograms are the fundamental data of phylogenetic biogeographic analysis. This finding is analogous to what is known about how including fossil taxa in phylogenetic analyses along with extant taxa can improve resolution and accuracy.
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The open availability of global scientific databases is key to advancing research of the Earth system and facilitating cross‐disciplinary studies. There are numerous data sets available for investigating tectonics, but none that provide an internally consistent representation of the structural framework, crustal architecture, and geodynamics. We present Reclus, a suite of global, integrated databases that fill this gap, thereby providing the community with the key components for investigating the Earth system. Reclus includes databases of the following: (a) structural elements, which define the three‐dimensional geometry of the rock volume, including folds and faults; (b) “crustal” facies describing the geometry and composition/rheology of the lithosphere; (c) igneous features; and (d) geodynamics, representing the dominant thermo‐mechanical processes acting on the lithosphere. These databases and workflows are applied to East Africa to investigate the geometry and heterogeneity of the margin and its hinterland. This margin is often summarized in the literature as a “transform margin,” represented by a single structural feature, the “Davie Fracture Zone,” but it is much more complicated. We show how the pre‐existing structure, the superimposition of successive tectonic cycles, and crustal heterogeneity dictate the complexity observed.
Chapter
Sedimentary basins have been increasingly regarded as mobile entities throughout the development of the geological sciences. The recognition of allochthonous terranes leads to the concept that the history of some sedimentary basins may be partly or entirely independent of the lithospheric plate in which they now occur. Allochthonous terranes are thought to be former oceanic plateaus, including sedimentary cover. These sediment accumulations are here named “inverse basins.” Inverse basins are marine or nonmarine sedimentary accumulations that record sedimentation on surfaces of high topographic relief relative to the surrounding areas. Allochthonous terranes are recognized mainly on the basis of biostratigraphic, lithostratigraphic, paleomagnetic and other geophysical data. Inverse basins associated with allochthonous terranes are of two classes: 1) those with fill that predates or is coeval with amalgamation or accretion; and 2) those that record post-amalgamation or post-accretion displacement and tectonics. Understanding terrane history prior to accretion depends primarily on recognition of latitudinally dependent magnetic, sedimentologic, and paleontologic features in the sediments of class-1 basins, posing challenging multi-disciplinary problems to the basin analyst.
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Tethys in its original meaning was understood by Eduard Suess as the ancient sea separating Angaraland from Gondwanaland. Contrasting to this paleogeographic conception, “Tethys” and “Tethyan” are currently used with different meanings in tectonics and paleo-biogeography. In paleobiogeography, Tethys is understood as a realm with varying extension. This dynamic conception is in contrast to the conception of the stable Cretaceous Mesogée by Dou-villé (1900).
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Eduard Suess (1831-1914) is one of the most widely misunderstood and miscited authors in the history of tectonics mainly because of the nature of his writings in which very detailed local descriptions are tightly interwoven with novel theoretical interpretations. Two short publications by him, an abstract with the title Ueber den Aufbau der mitteleuropaischen Hochgebirge (On the structure of the middle European high mountains) published in 1873 and a letter he wrote to the editor of the English translation of Das Antlitz der Erde, William Johnson Sollas and which was published as the 'Preface by the Author' to the translation in 1904, may be taken as guides to probe his thinking on tectonics by finding the continuous thread running through his publications pertaining to tectonics. In fact, it is quite impossible to understand what his basic tectonic picture was without being familiar with the 1873(a) abstract, which is never cited in the literature and has not yet been examined by historians of geology. After having read it, one has to understand then why Suess stuck to the contraction theory. The answer to that is in his letter to Sollas. Basically, Suess saw that mountain-building was a consequence of motions of discrete rigid to semi-rigid lithospheric blocks moving independently with respect to one another. While a block moved to shorten its frontal part, it caused extension in its wake. Such motions of independent blocks Suess likened to the motions of ice floes in drifting pack ice. When he considered global stratigraphy, he realised that the main transgressions and regressions were global and it was them that governed the dominant character of the stratigraphic time-table. Changing the capacity of ocean basins was the only way, Suess thought, to bring about transgressions and regressions. To do this, Constant Prevost's model of global contraction (not Elie de Beaumont's, accepted by Dana and Le Conte) provided the best mechanism. Prevost's model worked so well for stratigraphy that Suess felt that it had to be right also for tectonics. To use Prevost's contraction for mountain-building and rift-making, Suess had to assume different depths of detachments and irregular regions of attachment of one storey to the other along such detachments. Qualitatively, Suess' tectonic model was the best ever offered before plate tectonics and plate tectonics preserved many of its basic elements and even details of some of them.
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Biogeographic patterns are evaluated in Early Cambrian trilobites using a modified version of Brooks Parsimony Analysis. Analysis of patterns of vicariance yields three major biogeographic groupings: the first suggests area relationship between Siberia, parts of west Gondwana and regions marginal to it, and south-western Laurentia; the second suggests area relationship between Baltica, eastern Laurentia, and north-western Laurentia; and the third groups Antarctic and Australian faunas. The patterns of area relationship between south-western Laurentia and regions lying along the western part of Gondwana provides evidence for a vicariance event in trilobite evolution relating to the breakup of Pannotia; this implies that there was potentially a homogeneous group of trilobites distributed across Pannotia prior to its break up. As this supercontinent broke up between 600-550 Ma it suggests that trilobite cladogenesis predates, perhaps significantly so, the Cambrian radiation and the first appearance of trilobites in the fossil record. Based on the phylogenetic position of trilobites, a clade nested well within the Metazoa, this result from biogeography provides further support for the argument that the Cambrian radiation actually has fairly deep roots extending back at least into the late Neoproterozoic. Patterns of geo-dispersal were also evaluated and these were poorly resolved. This result suggests that the tectonic regime in the late Neoproterozoic and Early Cambrian which most influenced patterns of trilobite evolution was continental fragmentation leading to vicariance.
Article
The Geological Society of London Proposal for "...ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long held, but widely misunderstood distinction between these two essentially parallel time scales has been rendered unnecessary by the adoption of the global stratotype sections and points (GSSP-golden spike) principle in defining intervals of geologic time within rock strata." Our review of stratigraphic principles, concepts, models and paradigms through history clearly shows that the GSL Proposal is flawed and if adopted will be of disservice to the stratigraphic community. We recommend the continued use of the dual stratigraphic terminology of chronostratigraphy and geochronology for the following reasons: (1) time-rock (chronostratigraphic) and geologic time (geochronologic) units are conceptually different; (2) the subtended time-rock's unit space between its "golden spiked-marked" lower and upper boundaries, actually corresponds to the duration of the time-rock unit's defining geologic s.l. events-set; therefore, in no way can physical time (instants or intervals) be directly defined by GSSPs, (3) combining in a single system of "chronostratigraphic units" the time-rock and geologic time units as currently understood, leads to the epistemological error of uniting evidence (rock successions) with inference (the interpreted duration of chosen defining events); (4) the redundancy of the terms eonothem, erathem, system, series, and stage with eon, era, period, epoch and age lacks support, given that they are conceptually different; in fact, referring to "eon," "era," etc. as terms uniting both time-rock and geochronologic connotations will produce needless nomenclatorial confusion, attaching different meanings to already well known and widely used geologic terms; and (5) the reversion of 'geochronology' to its main stream and original meaning of numerical dating has no foundation, just by considering that the use of geochronolgy precedes numerical dating, which became practical by the 1960's. We endorse the following: (1) the GSSP network needs to be improved through the use of reference sections at high latitude sites, and in sedimentary continental rock successions of achievable, dependable positioning in the global standard timetable; and (2) to attend to researchers using astronomically-forced sedimentary systems, the designation of unit stratotypes needs to be reinstated as a valid and as a, complementary means of defining chronostratigraphic units, particularly at the stage and lower chronostratigraphic rank.
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A new genus, Tullypothyridina, type species T. venustula (HALL, 1867), is described from the late Givetian of central New York, Pennsylvania, eastern Kentucky, and probably eastern Iowa. The type species of the related genus Hypothyridina BUCKMAN, 1906, H. cuboides (SOWERBY, 1840), the name of which was originally and subsequently given to the American species, is discussed. The taxonomic definition of this late Givetian species from South Devon, its stratigraphic position, and its paleogeographic significance are examined. The type species of the genus Glosshypothyridina RZHONSNITSKAYA, 1978, G. procuboides (KAYSER, 1871), is also scrutinized; this late Eifelian species from the Eifel region has been considered as closely allied, when not identical, to both the American and English species.
Chapter
Geologists have not been content just to observe and describe. They have concurrently attempted to collate their observations, to formulate general principles or laws, and to build more comprehensive theories. Students of sedimentary deposits are no exception. The first efforts at interpretation of sediments were directed toward reconstruction of the environment of deposition at a particular time and place. With ever-widening comprehension, the efforts at interpretation have been extended to embrace longer periods of time and to include, at last, the whole basin in which the sediments in question were deposited. Consideration of the basin as a whole provides a truly unified approach to the study of sediments.
Article
Eduard Suess (1831-1914) is probably the greatest geologist who ever lived. He died 100 years ago and left us the modern geology as we know it. His work ranged from paleontology through stratigraphy, geomorphology, urban geology, finally to tectonics. His magnum opus was the multi-volume Das Antlitz der Erde (The Face of the Earth), the greatest book in the history of geology. It is a complete description of the geology of the planet from the viewpoint of the theory of thermal contraction in Constant Prévost’s version, as modified by Suess. For all the admiration it caused it has been largely left unread and as a consequence geology lost some half a century until the invention of plate tectonics in 1965. This was in part, because the way Suess wrote the book made reading very difficult. The following is not a biography of Suess, but a review and evaluation of his work during the centenary of his death.RÉSUMÉEduard Suess (1831-1914) est probablement le plus grand géologue qui ait jamais vécu. Il est mort il y a 100 ans et il nous a laissé la géologie moderne telle que nous la connaissons. Son oeuvre va de la paléontologie à la stratigraphie, la géomorphologie, la géologie urbaine, enfin jusqu’à la tectonique. Son magnum opus est le multi-volume Das Antlitz der Erde (La Face de la Terre), le plus grand livre de l’histoire de la géologie. C’est une description complète de la géologie de la planète du point de vue de la théorie de la contraction thermique dans la version de Constant Prévost, modifiée par Suess lui -même. En dépit de l’admiration dont il était l’objet , ce grand livre a été très peu lu. En conséquence la géologie a perdu près d’un demi-siècle jusqu’à l’invention de la tectonique des plaques en 1965. C’est en partie a cause de la façon dont Suess a écrit le livre qui rend la lecture très difficile. Ce qui suit n’est pas une biographie de Suess, mais un examen et une évaluation de son travail à l’occasion du centenaire de sa mort.
Article
The limits of Cascadia were first defined to contain nearly the entire margin of the Pacific Northwest, from Cape Mendocino through the Alaska Panhandle [Schuchert, 1910; Schuchert and Barrell, 1914]. Since that time, the boundary of Cascadia has shrunk to become essentially synonymous with the region where the Juan de Fuca plate subducts beneath the North American plate. As a consequence, seismic hazard assessments in the Pacific Northwest have conventionally focused on the potential for large megathrust earthquakes along the interface of the Juan de Fuca and North American plates.
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Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physio-chemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least similar to 60%-70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record, and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of significant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic- and mantle-plume-dominated processes. The 60%-70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires ongoing destruction (recycling) of crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination.
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Budantsev, L. Yu. (Komarov Botanical Institute, Prof. Popov Str. 2, 197376 St. Petersburg, Russia). Early stages of formation and dispersal of the temperate flora in the Boreal Region. Bot. Rev.58(1): 1–48, 1992.—The thesis of this review is that, as stated as early as 1908 by V. L. Komarov, the composition of a flora can be understood only as a process, or separate stage, in the context of migration in time and space of various floristic assemblages and their isolation, as induced by transformation of continental and ocean shapes, changes in climate, and the environment as a whole. Thus the formation of geofloras of the past was influenced by gradually changing environments that determined the spread, patterning, and spatial differentiation of floras and their evolution. Parallel to the more commonly-seen names of eras—Paleozoic, Mesozoic, and Cenozoic—we can speak of the Paleophytic, Mesophytic, and Cenophytic eras. Eras defined in these two ways (by faunistic or by floristic criteria) do not completely coincide. Generally, changes in the flora have, necessarily, preceded changes in the fauna. It is the Cenophytic with which this review is mostly concerned, the era of Angiosperm dominance. The movement of early subtropical and warm temperate floras in the Early Cenophytic, followed by temperate or even boreal floras, as the climate changes, is traced in detail. The regions discussed most fully are the Boreal-Atlantic and Boreal-Pacific, with emphasis on the Angaro-Beringian flora. The disappearance of archaic forms (e.g., cycadophytes) and the gradual predominance of angiosperms is documented. The movements of the floral assemblages in response to environmental changes are mapped and described. The early development and diversification of the boreal temperate flora is considered to have taken place mainly in Angaro-Beringia, associated with the invasive migration of tropical angiosperms from southeastern Asia.
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The Lower Silurian Medina Group from the Niagara Gorge at Lewiston, New York, contains one of the oldest known Llandovery palynomorph assemblages in North America. Age determinations using conodonts and brachiopods from the basal units of the overlying Clinton Group suggest that the Medina Group may be correlative with the Rhuddanian Stage of the Llandovery. A brief review of North American Lower Silurian series nomenclature is presented to place the Medina Group in a regional stratigraphic context. Previous recommendations that North American series nomenclature be replaced by the standard British Llandovery stages are followed.Well‐preserved acritarchs, chitinozoans, and spore‐like micro‐fossils have been recovered and described from the Whirlpool Sandstone, Power Glen Formation, and Grimsby Sandstone. Forty palynomorph species were recognized. Four new species and one new combination of acritarchs are proposed: Cymatiosphaera densisepta n. sp., Eupoikilofusa? rhomba n. sp., Micrhystridium? polorum n. sp., Retisphaeridium? fragile n. sp., and Moyeria cabotti n. comb. et emend.In addition to previously described spore‐like microfossils, two new genera, Strophomorpha and Vermiculatisphaera, and four new species are proposed: Nodospora retimembrana n. sp., Rugosphaera? cerebra n. sp., Strophomorpha ovata n. sp., and Vermiculatisphaera obscura n. sp.The Whirlpool Sandstone and lower part of the Power Glen Formation are dominated by spore‐like microfossils, whereas the upper part of the Power Glen and lower part of the Grimsby contain predominantly acritarchs. The palynomorphs recovered from these Lower Silurian near‐shore facies appear to have been controlled by the depositional setting and are compared to other Lower Silurian palynomorph assemblages from North America and Britain.
Article
Charles Schuchert developed the geosynclinal concept ofHall andDana into a paleogeographic model of North America which included “borderlands” on the oceanic side of each geosyncline. These lands were the source of thick clastic sediments which accumulated in the geosynclines. As early as 1841 H. D.Rogers inferred a southeastern source for clastic sediments in the Appalachian Mountains.Hall (1859) proposed that folded mountains form only where sediments have accumulated to great thickness in narrow bands along the margin of continents. Dana named such belts “geosynclinals”. He advocated a theory of continental growth by accretion of rocks around a primitive nucleus. In 1890 he recognized Archaean protaxes east of the Appalachians, west of the Rocky Mountains, and probably in the Cascade-Sierra Nevada range. C. D. Walcott showed Dana's Archaean highlands on maps which related the thickness of Cambrian deposits to times of submergence. H. S.Williams named the eastern land Appalachia in 1897. Details for other periods were mapped by B. Willis and by A. W. Grabau in 1909, neither of whom showed any western borderland. A series of maps for short time intervals bySchuchert (1910) show numerous positive areas including a large Cascadia west of the Cordilleran trough. Faunal relationships implied that the Appalachain geosyncline was largely isolated from the Atlantic Ocean during the Paleozoic. In 1923Schuchert insisted that geosynclines were part of the continent, not ocean margins nor mediterraneans, and that the sediments implied borderlands that had repeatedly been elevated and eroded.
Article
Some stratigraphers have recently insisted that for historical reasons, the Neogene (Miocene+Pliocene) should be extended to the present. However, despite some ambiguity in its application by Moriz Hörnes in the 1850s, the “Neogene” was widely adopted by European geologists to refer to the Miocene and Pliocene of Lyell, but excluding the “Diluvium” (later to become the Pleistocene) and “Alluvium” (later to become the Holocene).During the late 19th and early 20th centuries, the ends of the Neogene, Tertiary and Pliocene evolved in response to the progressive lowering of the beginnings of the Quaternary and Pleistocene. This evolution was a logical result of the widespread views that the most recent “ice ages” were worthy of recognition as a formal unit of the standard geologic time scale, and that the structure of this time scale must be strictly hierarchical.Motivations for the extension of the Neogene to the present include the desire to establish a monopoly for marine biochronology in the definition of standard global chronostratigraphic boundaries. This agenda would also eliminate the Tertiary, Quaternary, and Holocene. These changes are unnecessary. There is every reason to retain the traditional hierarchical structure of the Cenozoic time scale.
Article
Three fundamental questions have confronted paleoceanographers from the beginning of their North American explorations. What was the size and timing of ancient epicontinental seas: large and long-lasting or small and brief? What characterized the distribution of biotas and sediments at any one point in time: a multitude of complex facies patterns or a more spacially homogeneous cover? What promoted continental foundering: eustatic changes in sea level or relative changes in sea level brought about by regional tectonics? These questions have been debated by North Americans since the middle 1800s in response to various new insights, usually coming from abroad but often elaborated into substantial contributions of equal standing. Contemporary facies zones in Mediterranean biota found by the Englishman E. Forbes attracted the notice of geologists as early as 1844. C. Whittlesey was among the first to apply the bathymetric scheme of Forbes to the interpretation of American Paleozoic strata in 1851. The outstanding "native" innovation of the period was J. Hall's geosyncline concept, which is reflected in the earliest map of Paleozoic North America made by T. C. Chamberlin in 1881. Another wave of influence spread from the late 19th century work on stratigraphic facies patterns by the German J. Walther. A. W. Grabau is best remembered as Walther's foremost American champion against the formidable layer-caker E. O. Ulrich in the first decades of the 20th century, but he also made pioneering contributions of his own on Paleozoic sea level studies and global paleogeographic reconstructions. Charles Schuchert was the consummate paleogeographer of this period. Meanwhile, the term "cyclothem" was coined by J. Marvin Weller in 1930 for recurrent Carboniferous strata in Illinois. Controversy fast erupted over a glacial as opposed to tectonic mode of origin for these cycles. In 1964, A. B. Shaw restimulated interest in Paleozoic oceanography through his reformulation of Walther's ideas. Novel additions included a model for epeiric sea carbonates and the methodology for graphic correlation. Invoking studies by C. G. J. Petersen on recent communities in Danish waters, A. M. Ziegler added new emphasis to paleobathymetry based on fossil communities. As was in Grabau's case, this interest eventually led to larger concerns with global paleogeography. Although the same questions are still debated today, the foregoing periods set the stage for a modern, more interdisciplinary approach to Paleozoic oceanography.
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Extract There may be said to be two main branches of geological investigations the physical and the biological—not, of course, that these can be regarded as independent or divorced from each other, but to a certain point they can make their contributions independently. For a full history, the physical and the biological changes must be known and their mutual relationship understood. It seems possible, however, that the physical history of the earth is likely to be known in much greater detail than that of the fauna and flora, for the “dry lands,” tenanted as they undoubtedly were by various forms of life, have left behind a record which can be fairly well traced on the physical side but will always refuse to yield up all its secrets on the biological side, since only rarely have the land animals and plants been preserved by a lucky chance in the rocks accumulating at the time of their existence. The permanence of continents and ocean-basins has long been a subject of controversy. Lyell, in his “Principles of Geology,” makes reference to the early ideas of the Mediterranean peoples on this subject, while Lyell himself was of opinion that continents and ocean-basins do change places in the course of ages. This idea was early challenged by both physicists and biologists. The physicists, led by Lord Kelvin, regarded the general framework of the earth as having been fixed in very early times, and Kelvin considered that the oceans and continents may have been mapped out ...
Article
Sedimentation rates combined with stratigraphical correlation provided the earliest reasonably objective geological time-scales, but these were at best crude approximations. Later, sedimentation rates were used only to interpolate between radiometrically determined ages. The hypothesis that average maximum rates of sedimentation (or subsidence) have increased during Phanerozoic time is discussed and it is concluded that the evidence for it is unsatisfactory.
Article
The shales under discussion contain regularly-spaced thin bituminous laminae alternating with mineral layers, which probably represent varves.The distribution of particulate organic matter in the sea is briefly reviewed. Phytoplankton productivity is highest in regions of upwelling and in continental shelf waters, where in addition there is generally a significant proportion of detritus from terrestrial plants and benthonic algae. Only a small fraction of this organic matter reaches the sea floor and of this very little is ultimately preserved in marine sediments, principally as kerogen. The proportions of terrestrial and marine components of the organic matter in sediments can be determined in several ways.The organic content tends to be highest in fine-grained sediments laid down in poorly-oxygenated or anaerobic waters, characteristically in the deeper parts of nearshore basins partly isolated from normal oceanic circulation by sills. Certain sediments laid down in very shallow lagoons may also be rich in organics. No simple relationship of organic content and depth of sea is discernible.In interpreting bituminous shales in the stratigraphic record, comparisons with the present may be somewhat misleading. For long periods in the past the world climate was apparently more equable than today and shallow shelf seas more extensive. It is argued, taking examples from the Jurassic of Europe and the Devonian of North America, that the familiar “barred basin” model may be inapplicable to many bituminous shales in the past, which were relatively shallow-water deposits laid down in quiet but not invariably stagnant water below wave base. Certain geosynclinal graptolitic shales may have been laid down in deep water, though perhaps shallower than the associated greywackes.
Article
Three marine benthic faunal realms can be recognized in the Early and Middle Devonian. The Eastern Americas Realm consisted of most of the eastern half of North America and South America north of the Amazon. This realm extended in a southwest direction from the Devonian equator to approximately 35°S and was an isolated epicontinental sea during much of its history. The Eastern Americas Realm was bounded on the west by the Transcontinental Arch, on the north by the Canadian Shield and on the east and southeast by a peninsular extension of the Old Red Continent. These barriers were emergent during much, but not all, of Devonian time. Seaways beyond these barriers belonged to the Old World Realm. The Malvinokaffric Realm that was farther south was apparently temperate to arctic in climate and latitudinal position and contained few corals.Rugose corals in the Eastern Americas Realm show increasing generic-level endemism from the Late Silurian through the Early Devonian; during the late Early Devonian, 92% of the rugosan genera are not known anywhere else in the world. Endemism decreased through the Middle Devonian to zero in the early Late Devonian. The Early Devonian increase in endemism paralleled, and was probably related to, the development of the Old Red Continent as a barrier between America and Africa—Europe. The waning of endemism in the Middle Devonian reflects the breaching of the land barriers. This permitted some migration in and out of the realm in early Middle Devonian time but greatest movements were in late Middle Devonian time. Principal migration directions were from western or Arctic North America into the Michigan-Hudson Bay area and from the southern Appalachian area into Africa.
Article
A geomorphologist, William Morris Davis, founded the Association of American Geographers in 1904. Today, a century later, it is timely to reflect on the nature of geomorphology so long ago, on paths taken and paths ignored. By 1904, the heroic age of American geomorphology, of the western explorations, had passed. Powell was dead, Dutton was retired and ill, and Gilbert seemed destined at the time for lonely retirement. In their stead, Davis strode the field like a colossus. His cycle of erosion, nurtured for 20 years, fit well into the evolutionary dogma of the age. With its emphasis on time, the perceived relevance of structure and process atrophied. While Earth's main relief features were still attributed mainly to a cooling and contracting planet, Dutton's isostasy and Taylor's mobilism received short shrift. In any case, depending on who one believed, Earth was only 20 to 400 million years old. Furthermore despite advances in mechanics and applied sciences, geomorphic processes were largely ignored. This was soon to change—from an expanding time scale based on radioactive decay, a reinvigorated Gilbert's field studies and flume experiments, Udden's work on wind, and advances in geodesy, geophysics, hydrology, and scientific methodology. That these advances lingered so long in the wings was more a reflection of the restrictive Davisian stage than of the many paths potentially open to geomorphology as the 20th century dawned.
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The Yukon Territory provides a setting for its fauna of particular historical and ecological interest. Much of the Yukon was unglaciated in Pleistocene time as part of Beringia, a much larger ice-free but essentially treeless area extending through Alaska into eastern Siberia, and this whole area was cut off from the rest of North America by ice sheets. After deglaciation the Yukon was again connected to the North American continent, allowing for movements by and contacts with other faunas. The Yukon today is a distinctly northern region dominated by arctic, alpine, subarctic and boreal terrain. Nevertheless, it is relatively benign for its latitude of 60 - 69°N, and habitat diversity is enhanced by the local amelioration of temperature on south-facing slopes and in river valleys. As a result of these past and current influences, the insect fauna of the Yukon is relatively rich and distinctive, reflecting the results of evolution on a variety of scales, and comprising distinctive forest, grassland, tundra and other species. The composition of the fauna reflects the current or past prevalence of particular habitats, such as boreal forest (which supports many widely distributed North American species), shallow still waters (which support many aquatic species) and dry grasslands on warm slopes (which support many leafhoppers and heteropterans, for example). The groups reported on in this book contain about one third of the known arachnid fauna of Canada and more than half of Canada's insect fauna. In these groups, 297 species of spiders, 157 species of mites, and 2711 species of insects—or about one fifth of the Canadian species known in those groups—are recorded in the Yukon, suggesting that in total more than 6000 species of insects and 900 species of arachnids occur there. Individual species as well as different groups differ widely in ecological and distributional features according to their particular histories. However, the fauna, like the terrain, is distinctly northern; it is dominated by certain northern and widespread taxa, whereas other groups are represented by few species. The prevalence of northern groups tends to be correlated, though by no means exclusively, with their occupation of aquatic habitats (relatively favourable in the north) and with general feeding habits such as predation (relatively advantageous where specific resources are more limited). Many adaptations of structure, behaviour and life-cycle reflect the demands of cold and seasonal life zones. Overall, nearly twice as many Yukon species of insects are restricted to the Nearctic region as occur in both Nearctic and Palaearctic regions, though a few northern groups, as well as spiders and oribatid mites, have many Holarctic species. Much taxonomic evidence, such as the occurrence of sister species in the Yukon and in Asia, indicates past connections between North America and Eurasia that preceded the well known Pleistocene connection. About half of the Nearctic species of the Yukon are widespread in North America, and one third are western. These and other ranges suggest that species have come to occupy the Yukon by several different routes. For example, northern boreal ranges predominate among the Nearctic species. Therefore, many of them probably are postglacial invaders from the south and east. However, other widely distributed arctic and boreal species are known from Beringia as Pleistocene fossils, reflecting their presence there during glaciation. Several species appear to have survived the Pleistocene in both Beringian and southern refugia, because they have distinct or disjunct northern and southern populations. In several groups substantial numbers of species occur only in the (glaciated) southern parts of the Yukon and have not spread farther north; they are presumed to have entered the Yukon from the south after
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Magnetic susceptibility (k) and intensity of remanent magnetisation (J) logs can be used for chronostratigraphic correlation of the late Holocene stratigraphic sequence of the southern basin of Mara Lake. Q-ratio (J/k) logs also show a good correlation from core to core within the lake basin.Chronostratigraphic correlations of cores from Mara, Shawnigan and Christina Lakes were carried out on the basis of paleodeclination and paleoinclination log information and substantiated by the relative position of the Mt. Mazama tephra in the Mara and Shawnigan Lake stratigraphic sequences. This information was used as dating control to construct and compare magnetic susceptibility, intensity of remanent magnetisation and the Q ratio record for each of the three lakes. None of these three parameters would appear to be useful for correlation from lake basin to lake basin. Therefore, on the basis of this study magnetic susceptibility, intensity of remanent magnetisation and Q ratio logs can be used for intra-lake basin correlation but not for lake to lake correlation.
Article
The paleodeclination and paleoinclination logs compiled from the cores taken from Mara Lake show consistent, well defined oscillations. It was hoped that the Mt. St. Helens and Mt. Mazama tephra layers encountered in the cores would provide accurate, absolute dating control of the cores as well for the paleodeclination and paleoinclination logs. Unfortunately the dates of 3300 BP for the Mt. St. Helens tephra and 6845 50 BP for the Mt. Mazama tephra are incompatible with a constant rate of sedimentation. It would appear that the Mt. Mazama date is valid and a redetermination of the Mt. St. Helens date based on the 6845 50 BP date for the Mt. Mazama tephra and a constant rate of sedimentation from Mazama time to the present gives a date of 4100 BP for the Mt. St. Helens tephra. This dating control has been used to construct paleodeclination and paleoinclination logs versus time which correlate well with paleomagnetic logs from Fish Lake, Oregon and Shawnigan Lake on Vancouver Island.
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This paper is one of a series that commemorates the fiftieth anniversary of the founding of the Society of Economic Paleontologists and Mineralogists in 1926. At that time, thought about tectonics and sedimentation was dominated by the ruling hypothesis of continental accretion. Marginal geosynclines were thought to have been filled with sediments derived from borderlands of Precambrian rocks, and then welded tectonically to the continent. In the 1930s, the fundamental distinction noted by Bailey and Jones between graded graywacke- graptolitic slate suites and cross-bedded sandstone-shelly carbonate suites provided a prelude to Krynine's petrographic-tectonic sandstone clans. In the 1940s sedimentary petrography finally emerged from its heavy mineral era to broaden its vistas. Prior notions of evolutionary successions of sediment types linked to a supposed tectonic cycle (e.g. the European ophiolite-flysch-molasse sequence) became more explicit. Refinements of sandstone classifications by Folk, Pettijohn, Gilbert and others, coupled with Krynine's tectonic cycle and the stratigraphic syntheses of Krumbein, Sloss, Dapples, and others, led in the 1940s to the belief that tectonics is the ultimate sedimentary control.
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Thesis (Ph. D.)--Columbia University, 1912. Slip with thesis note prefixed and one leaf with "Vita" inserted at end. Vita and thesis note also on p. [4] of cover. At head of title: Annals of the New York academy of sciences, vol. XXII. Published also in the Annals without thesis note. Bibliography: p. 105-112.
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