bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and temporal patterns of macroboring within Mesozoic and Cenozoic coral reef systems
Authors: Perry Christopher T. , Bertling Markus 
Published: April 2008

Abstract
Macroboring of coral reefs has varied significantly through time, with the modern intensity and producer composition (usually dominated by sponges) as a rather recent phenomenon. Given the outstanding role and influence of bioerosion on framework morphology, community composition and sediment production, Modern conditions are therefore poor analogues for the structure and function of pre-Neogene reef systems. Modern and Neogene reef borer associations are mostly dominated by sponges, although marked spatial variations in the abundance of borer groups are evident within individual reef systems. Highest diversity typically characterizes low energy, shallow water back-reef or lagoon sites. This condition evolved gradually from the Late Triassic onwards, when scleractinians first built reefs.
Sponges appear to have played a subordinate role in Mesozoic coral-dominated buildups. Worms and barnacles dominate in the early Mesozoic (Triassic and Lower Jurassic), with a progressive increase in bivalve borers through the Jurassic. The paucity of data collected to date makes determination of the causes of temporal change in macroboring community composition difficult to constrain. Macroboring groups seem to have withstood biotic crises much better than their coral substrate and thus reef ecological evolutionary units are not applicable. There is some indication that macroborers may have radiated to colonize new ecological niches during the early stages of coral reef diversification. The development was nonetheless influenced by biotic changes in the marine realm, the strongest effects potentially resulting from switches in nutrient status and the origin or diversification of reef grazers.
El Niño-Southern Oscillation mass mortalities of reef corals: a model of high temperature marine extinctions?
Authors: Glynn Peter W. 
Published: April 2008

Abstract
Protracted high sea temperature anomalies accompanying El Niño-Southern Oscillation (ENSO) events have caused reef-building coral bleaching (loss of zooxanthellae) and mortality in all major coral reef biogeographic regions during the past two decades. Coral reef degradation in the eastern tropical Pacific has resulted from reductions in live coral cover, declines in coral species population abundances, local to regional scale extinctions, disruption of predator/prey spatial relations and relative abundances, bioerosion of reef frameworks, and low coral recruitment. None of the coral species that have suffered regional extinctions has reappeared after 15 years. Intense external and internal bioerosion by fishes, echinoids, lithophagine bivalves and clionid sponges has occurred on reefs affected by the 1982/83 El Niño coral bleaching event, and 1000–5000 year old reef framework accumulations in the Galápagos Islands have been completely eroded and reduced to gravel and sand. Because tropical zooxanthellate reef species are more vulnerable to rising (2–3°C) than falling (8–10°C) temperatures, greenhouse conditions may be more critical in limiting reef growth than icehouse conditions. ENSO warming episodes elicit physiological stress responses resulting in widespread mass coral mortality, leaving scant traces relating to causation. Signals that may help to identify past ENSO disturbances are: (a) temperature-related oxygen isotopic signatures, (b) skeletal stress bands and growth discontinuities, (c) coral debris in beach storm deposits, (d) increases in coral clastics resulting from intensified bioerosion and (e) the skeletal elements of bioeroders. Because this disturbance is the most pronounced and widespread of any known natural perturbation, and may increase markedly in scope with projected global warming predictions, it is considered a likely agent of future and possibly some ancient bioevents.
Palaeomagnetism and Palaeozoic palaeogeography of Gondwana and European terranes
Authors: Tait Jenny , Schätz Michael , Bachtadse Valerian , Soffel Heinrich 
Published: April 2008

Abstract

Neoproterozoic to Late Palaeozoic times saw the break-up of the supercontinent Rodinia, and the subsequent construction of Pangaea. The intervening time period involved major redistribution of continents and continental fragments, and various palaeogeographical models have been proposed for this period. The principal differences between these models are with regard to the drift history of Gondwana, the timing of collision between northern Africa and Laurussia, and formation of Pangaea. Palaeomagnetic evidence provides basically two contrasting models for the Ordovician to Late Devonian apparent polar wander (APW) path for Gondwana involving either rapid north and southward movement of this continent, or gradual northward drift throughout Palaeozoic time. In contrast, palaeobiogeographical models suggest contact between Laurussia and Gondwana as early as mid-Devonian time with the continents basically remaining in this configuration until break-up of Pangaea in the Mesozoic era. This is in conflict, however, with most palaeomagnetic data, which demonstrate that in Late Devonian time, north Africa and the European margin of Laurussia were separated by an ocean of at least 3000 km width. This is also in agreement with the geological record of present-day southern Europe, which argues against any collision of northern Africa with Europe in Devonian time. With regard to formation of Laurussia, however, palaeobiogeographical and palaeomagnetic data are in excellent agreement that by mid-Devonian time the oceanic basins separating Baltica, Laurentia, Gondwana-derived Avalonia and the Armorican Terrane Assemblage (ATA) had all closed. Palaeomagnetic and geological data are also in agreement that the Palaeozoic basement rocks of the European Alpine realm formed an independent microplate, which was situated to the south of Laurussia. In Late Silurian times it was separated by an ocean of
c.
1000 km, and by Late Devonian time was approaching the southern Laurussian margin. According to palaeomagnetic data, the northern margin of Gondwana was still further to the south in Late Devonian time, and according to the geological record in southern Europe, the main continent-continent collision of northern Africa with European Laurussia and closure of the intervening ocean occurred in Late Carboniferous times. Location of this suture is situated to the south of the Palaeozoic alpine units (e.g. the Greywacke zone, Carnic Alps, Sardinia and Sicily), but has been obscured by younger deformational events and cannot be precisely positioned. Assessing available evidence and as discussed in the text, it is proposed that the most likely scenario is that the northern margin of Gondwana drifted gradually northwards from Ordovician to Late Carboniferous times when it collided with Laurussia, resulting in formation of Pangaea.
The mid-European segment of the Variscides: tectonostratigraphic units, terrane boundaries and plate tectonic evolution
Authors: Franke W. 
Published: April 2008

Abstract
The mid-European segment of the Variscides is a tectonic collage consisting of (from north to south): Avalonia, a Silurian-early Devonian magmatic arc, members of the Armorican Terrane Assemblage (ATA: Franconia, Saxo-Thuringia, Bohemia) and Moldanubia (another member of the ATA or part of N Gondwana?).
The evolution on the northern flank of the Variscides is complex. Narrowing of the Rheic Ocean between Avalonia and the ATA occurred during the late Ordovician through early Emsian, and was accompanied by formation of an oceanic island arc. By the early Emsian, the passive margin of Avalonia, the island arc and some northern part of the ATA were closely juxtaposed, but there is no tectonometamorphic evidence of collision. Renewed extension in late Emsian time created the narrow Rheno-Hercynian Ocean whose trace is preserved in South Cornwall and at the southern margins of the Rhenish Massif and Harz Mts. Opening of this ‘successor ocean’ to the Rheic left Armorican fragments stranded on the northern shore. These were later carried at the base of thrust sheets over the Avalonian foreland. Closure of the Rheno-Hercynian Ocean in earliest Carboniferous time was followed by deformation of the foreland sequences during the late lower Carboniferous to Westphalian.
Closure of narrow oceanic realms on both sides of Bohemia occurred during the mid- and late Devonian by bilateral subduction under the Bohemian microplate. In both these belts (Saxo-Thuringian, Moldanubian), continental lithosphere was subducted to asthenospheric depths, and later partially obducted. Collisional deformation and metamorphism were active from the late Devonian to the late lower Carboniferous in a regime of dextral transpression. The orthogonal component of intra-continental shortening produced an anti-parallel pair of lithospheric mantle slabs which probably joined under the zone of structural parting and became detached. This allowed the ascent of asthenospheric material, with important thermal and rheological consequences. The strike slip displacements were probably in the order of hundreds of kilometres, since they have excised significant palaeogeographic elements.
The eastern termination of the Variscides: terrane correlation and kinematic evolution
Authors: Franke Wolfgang , Żelaźniewicz Andrzej 
Published: April 2008

Abstract
Analysis of tectonostratigraphic units in the West Sudetes reveals the same geological events as in the areas west of the Elbe Fault Zone: a late Proterozoic (Cadomian) orogenic event, Cambro-Ordovician to Devonian rift-drift, and late Devonian to early Carboniferous subduction-collision. There is no conclusive evidence of an Ordovician orogenic event. Tectonic units in the Sudetes are shown to be related to terranes defined in western parts of the Bohemian Massif. The Lausitz-Izera Block, the Orlica-Śnieżnik Unit and the Staré Město Belt represent easterly continuations of the Saxo-Thuringian Terrane. The Rudawy Janowickie Unit and the Sudetic Ophiolite contain fragments of the Saxo-Thuringian Ocean. The protoliths of the Görlitz-Kaczawa Unit, the South Karkonosze Unit, the Góry Sowie and the Kłodzko Units either belong to the Bohemian Terrane or else were welded onto it during mid-late Devonian metamorphism and deformation. Relicts of the Saxo-Thuringian Foreland Basin are marked by flysch with olistoliths in the Görlitz-Kaczawa Unit and in the Bardo Basin. The spatial array of terranes in and around the Bohemian Massif reveals a disrupted orocline, dissected by dextral transpression along the Moldanubian Thrust. This orocline was formed when central parts of the Variscan belt were accommodated in an embayment of the southern margin of the Old Red Continent.
The Baltica-Gondwana suture in central Europe: evidence from K-Ar ages of detrital muscovites and biogeographical data
Authors: Belka Z. , Ahrendt H. , Franke W. , Wemmer K. 
Published: April 2008

Abstract
The Lysogory Unit, the Malopolska Massif and the Upper Silesian Massif in southern Poland are parts of a mosaic of contrasting crustal fragments separating the old Precambrian crust of the East European Platform (EEP) from the Phanerozoic mobile belts of western Europe. The geological histories of these blocks are markedly different. They have been regarded as integral parts of the palaeocontinent of Baltica (that is, the EEP), mostly because of presence of fossils typical for the Baltic realm, although geophysical and geological data and some faunal elements rather suggest linkages to the Peri-Gondwana plates. To provide additional constraints for the plate tectonic affinity of these blocks detrital muscovite grains extracted from Cambrian and Devonian clastic rocks were dated by the K-Ar method. The K-Ar cooling ages show a very complex provenance pattern for clastic material in Cambrian time. Combined with the biogeographical constraints, the new provenance data apparently show that the blocks of Lysogory, Malopolska, and Upper Silesia are in fact crustal fragments derived from the Gondwana margin, not displaced parts of the East European Craton. Thus, the Teisseyre-Tornquist Line (that is, the edge of the EEP) is the Baltica-Gondwana suture in central Europe. The combined data reveal an accretionary scenario in which the Malopolska Block was the first Gondwana-derived microplate that accreted to the margin of Baltica.
The Brunovistulian: Avalonian Precambrian sequence at the eastern end of the Central European Variscides?
Authors: Finger F. , Hanžl P. , Pin C. , von Quadt A. , Steyrer H. P. 
Published: April 2008

Abstract

An outline is presented of the present state of research on the Precambrian evolution history of the Brunovistulian, a large (30 000 km
2
), mainly sediment covered Peri-Gondwana basement block at the eastern end of the Central European Variscides. On the basis of recent chemical, isotopic and geochronological data it is argued that the eastern half of the Brunovistulian (Slavkov Terrane) originated in an island-arc environment, documenting the rare case of Neoproterozoic crustal growth in central Europe. The western half of the Brunovistulian, the Thaya Terrane, includes more mature, recycled cratonic material and is considered to have been originally part of the Neoproterozoic Gondwana continent margin. A phase of regional metamorphism at
c.
600 Ma, followed by extensive granitoid plutonism, probably marks the stage when the Slavkov Terrane was accreted to the Thaya Terrane by arc-continent collision. A belt of metabasites, which is intercalated between the two terranes, may represent relics of the incipient arc or a back-arc basin. A comparison of geochronological data shows that the timing of geological events recorded in the Brunovistulian does not correlate with the evolution history of the Cadomian crust in the Teplá-Barrandian zone and the Saxo-Thuringian belt. This supports the theory that the Brunovistulian is not part of Armorica but derived from a different sector of the Neoproterozoic Gondwana margin. A correlation with the Avalonian superterrane appears feasible.
Deformation, metamorphism and exhumation: quantitative models for a continental collision zone in the Variscides
Authors: Seyferth M. , Henk A. 
Published: April 2008

Abstract

Two-dimensional thermo-mechanical finite-element models are used to gain a quantitative insight into the complex strain partitioning in continental collision zones. If models with Moho temperatures of 700–900 °C, as is indicated by petrological data, are simulated, frequently used flow laws for the lower crust cannot reproduce significant crustal thickening. Instead, decoupling between crust and mantle occurs, resulting in the widening of a diffuse deformation zone. To reproduce observed petrological data and orogen geometries, a stronger lower crust, with viscosities between 10
21
and 10
23
Pa s, is required. Models are applied specifically to a collision zone from the Variscan Orogen of Central Europe to understand the tectonometamorphic history, strain partitioning within the collision zone, as well as the rapid synconvergent exhumation of metamorphic complexes. Model predictions agree with the observed distribution of peak metamorphic conditions and show systematic variations of contemporaneous pressure-temperature (
P-T
) paths across the collision zone.
Turbidite basin and mass dynamics related to orogenic wedge growth; the Rheno-Hercynian case
Authors: Ricken W. , Schrader S. , Oncken O. , Plesch A. 
Published: April 2008

Abstract

Investigation of the Rheno-Hercynian Turbidite Basin suggests an interrelation between orogenic wedge migration and changes of the basin architecture, facies types and progradation rates of turbidite systems. The orogenic wedge was built dominantly by the Mid-German Crystalline Rise and accreted older parts of the Rheno-Hercynian Turbidite Basin. Turbidite sequences seem to have developed in stepwise prograding sub-basins. They show systematic trends of widely correlative (tens of kilometres) large-scale cycles that show an upward transition from coarse-grained clastics to highly diluted mud turbidites with highstand shedding of carbonates. These observations suggest the existence of accommodation cycles on the assumed shelf along the Mid-German Crystalline Rise. Exposure of the shelf above sea level was associated with bypass and transport of coarse-grained clastics into the basin, whereas flooding is thought to have caused storage of clastic deposits on the shelf and the simultaneous deposition of mud turbidites in the basin. Accommodation cycles, estimated to reflect an average duration of 10
5
–10
6
a, were probably related to cyclic changes of underthrusting in the internal parts of the orogenic wedge with concomitant uplift. The lifetime and onset of new sub-basins, of the order of a few million years, may show stages of imbricate fan formation. A pattern of major change in sedimentation rates, basin geometry and subsidence style of the Rheno-Hercynian Turbidite Basin and the Sub-Variscan Molasse Basin was interpreted to reflect the different change in crustal strength. This occurred because the hinge line between previously rifted and unrifted crust was overrun during wedge progradation. Numerical mass balance that compares exhumed and intra-basinal masses of the Rheno-Hercynian Turbidite Basin, including the proportional fill of the Sub-Variscan Molasse Basin and the Saar-Nahe Basin, indicates a significant lack of sediment mass (i.e. more than one-third of the exhumed masses). In this estimate, syn- to post-depositional truncation was included. As extension in the internal parts of the orogenic wedge has only a minor role, the above deficit is probably related to subduction of sediment during the early stages of convergence.
Upper-plate deformation during collisional orogeny: a case study from the German Variscides (Saxo-Thuringian Zone)
Authors: Schäfer Frauke , Oncken Onno , Kemnitz Helga , Romer Rolf L. 
Published: April 2008

Abstract
A doubly vergent orogenic wedge system within the Central European Variscides developed during Carboniferous collision of two continental fragments, the northwestern edge of the Saxo-Thuringian upper plate and the Rheno-Hercynian passive margin in the lower plate. The resulting thrust system in the upper plate above the SE-dipping subduction zone retains the memory of the mode of deformation partitioning and material flow pattern in its internal architecture, its kinematic, metamorphic and geochronological record, and its reflection seismic image. New data indicate a stepwise SE-ward progradation of the NW Saxo-Thuringian fold belt with two stages of shortening between about 340 and 335 and between 320 and 310 Ma above a NW-dipping basal detachment. The NW Saxo-Thuringian fold belt is reinterpreted as a retro-wedge that was kinematically coupled to the Rheno-Hercynian pro-wedge and subduction system. The two steps in retro-wedge growth are linked to (a) the onset of collision with the Rheno-Hercynian margin causing upper-plate uplift and (b) a widespread late-orogenic stage of wedge thickening. The retro-wedge accumulated mostly diffuse shortening of > 100 km versus the shortening by imbrication of 180–200 km in the Rheno-Hercynian lower plate. Material advection and orogenic architecture were strongly affected by asymmetric erosional removal towards the lower-plate foreland and by transient mechanical properties of the wedge system.
Geophysical constraints on exhumation mechanisms of high-pressure rocks: the Saxo-Thuringian case between the Franconian Line and Elbe Zone
Authors: Krawczyk C. M. , Stein E. , Choi S. , Oettinger G. , Schuster K. , Götze H.-J. , Haak V. , Oncken O. , Prodehl C. , Schulze A. 
Published: April 2008

Abstract
Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Granulite Massif, Erzgebirge) are investigated using a variety of geophysical methods (seismic reflection and refraction survey, magnetotelluric studies, gravity modelling). The Saxonian Granulite Massif and the Erzgebirge are not a continuous feature, as can be seen from discontinuous reflections, offset of upper-crustal seismic refraction velocity layers, and crustal resistivity increasing towards the Erzgebirge. Their juxtaposition during the evolution of two Variscan-age thrust wedges may have controlled this geometry. The earlier thrust wedge emplaced the supracrustal Erzgebirge HP nappes from the southeast to the northwest onto the Saxo-Thuringian Basin, whereas the later one propagated southwards and uplifted the Saxo-Thuringian granulites from deeper levels. To the southwest, the granulites are observed at shallow depth as far as the Franconian Line; to the southeast they extend down to the Moho, or they continue at mid-crustal levels. The granulites beneath the Saxo-Thuringian Belt can only have originated in one of two subduction zones: either through ‘subduction erosion’ and subsequent underplating of parts of the Saxo-Thuringian Plate from the north, or by intracrustal plug flow of overheated material from the southeast.
Foreland-directed lower-crustal flow and its implications for the exhumation of high-pressure-high-temperature rocks
Authors: Henk Andreas 
Published: April 2008

Abstract

Thermo-mechanical finite element models are used to study foreland-directed lower-crustal flow as a potential process to transport high-pressure-high-temperature (HP-HT) rocks from a continental collision zone to areas that have never experienced crustal thickening or deep burial. The numerical simulations show that lower-crustal rocks can indeed flow over substantial horizontal and vertical distances, provided a thermal anomaly reducing lithospheric strength exists in the foreland. As lower-crustal flow is a fast process compared with conductive heat transport and occurs subparallel to the isotherms, the resulting
PT
path of the rocks exhumed will be characterized by near-isothermal decompression. Modelling results are applied to the Saxonian Granulite Massif in Eastern Germany, where HP-HT granulites have been exhumed beneath a marine sedimentary basin during the Variscan Orogeny.
Hybrids, magma mixing and enriched mantle melts in post-collisional Variscan granitoids: the Rastenberg Pluton, Austria
Authors: Gerdes A. , Wörner G. , Finger F. 
Published: April 2008

Abstract
The composite Rastenberg Pluton in the South Bohemian Massif preserves an example of generation of relatively homogeneous granitoid hybrids by mixing of mafic and felsic magmas. Metaluminous melagranites and quartz monzonites, the main lithologies of the pluton, are interpreted to be hybrids. In contrast, a slightly peraluminous biotite granodiorite is considered to be a lower-crustal melt. In addition, abundant mafic ultrapotassic enclaves, country-rock lamprophyres and quartz monzodiorite bodies represent distinct lithospheric mantle-derived magmas, which were only slightly modified by fractionation and/ or magma mixing. Almost continuous linear chemical and isotope correlations joining the enclaves, quartz monzonites, melagranites and granodiorites indicate the importance of a mixing process in the generation of these rocks. Incompatible elements decrease with increasing silica and moderate negative Eu anomalies disappear towards the granodioritic endmember. Pb, Sr and Nd isotopes show typical crustal values in all granitoids but are more radiogenic in the ultrapotassic endmember. In the Rastenberg Pluton, the interaction of mantle- and crustal-derived magmas has produced unequivocal petrographic, chemical and isotopic evidence for mixing and mingling. Because similar features are lacking in most other Variscan plutons, we suggest that mantle magmas were not substantially involved in their genesis. Nevertheless, small-volumes of hybrids, involving variably enriched mantle-derived melts, do crop out locally throughout the central Variscides. In view of the generally strongly enriched nature of these small volume hybrid magmas, we suggest that voluminous mantle melting and large-scale magmatic underplating are unlikely to have occurred.