bluuebunny/crossref_metadata_2025_split huggingface dataset:
Timing of the Avalonia-Baltica plate convergence as inferred from palaeogeographic and stratigraphic data of chitinozoan assemblages in west Pomerania, northern Poland
Authors: Samuelsson Joakim , Vecoli Marco , Bednarczyk Wiesław S. , Verniers Jacques 
Published: April 2008

Abstract
Tectonically disturbed Ordovician rocks penetrated by deep drillholes in Pomerania, NW Poland (Koszalin-Chojnice Zone) belong to the Heligoland-Pomerania Deformation Belt. Earlier data demonstrate that the Avalonia-Baltica collision occurred in Late Ordovician times, but in Pomerania, the timing of convergence has not been ascertained, and it is uncertain if the rocks underneath the Koszalin-Chojnice Zone belong to Avalonia or Baltica. Data from chitinozoans, organic-walled Palaeozoic microfossils with applications in biostratigraphy and palaeobiogeography, were assessed from ten boreholes (Brda 2; Brda 3; Chojnice 5; Karsina 1; Kościernica 1; Nowa Wieś 1; Okunino 1; Sarbinowo 1; Skibno 1; Wyszebórz 1) to address these problems. The results improve the biostratigraphy of the cores and demonstrate that the youngest Ordovician rocks are of a Burrellian (early mid Caradoc) to Cheneyan (late mid Caradoc) age. Because these rocks are interpreted as forming part of the deformation belt, the obtained ages put a lower age limit on the initiation of foreland basin sedimentation on the foreland of the orogeny, i.e. the Baltic platform. Quantitative comparison of chitinozoan assemblages demonstrates a high level of similarity between Pomerania and Avalonia. Together, Pomerania and Avalonia show greater similarity to Baltoscandia than to North Gondwana, supporting the idea that the Tornquist Ocean had narrowed significantly in early Caradoc times.
Structure and evolution of the Bohemian Arc
Authors: Franke W. , Żelaźniewicz A. 
Published: April 2008

Abstract
Tectonic zones and palaeogeographic units (terranes) in the German segment of the Variscides correlate with equivalents in the Sudetes at the NE margin of the Bohemian Massif. This correlation defines an arcuate structure with an opening angle of about 90°. The structure is truncated to the SE by a crustal scale. NE-trending fault zone with dextral transpression, the Moldanubian Thrust (MT). The arc cannot have been formed by northeastward indentation of the Bohemian Massif, since there is no evidence of a fault zone on the NW flank of the notional indenter, and little evidence for northeastward tectonic transport. Kinematic and age constraints on the main fault zones instead suggest that the structural array was formed by a complex sequence of events. Northwestward displacement along the margin of the East European Platform (EEP) with clockwise rotation was followed by large southwestward movements along the Moldanubian Thrust, and renewed northwestward displacement along the SW margin of the East European Platform.
Late Quaternary architecture of trough-mouth fans: debris flows and suspended sediments on the Norwegian margin
Authors: Taylor J. , Dowdeswell J. A. , Kenyon N. H. , Ó Cofaigh C. 
Published: April 2008

Abstract
Trough-mouth fans are the main marine depocentres for glacier-derived sediments in the Polar North Atlantic, but their growth through the Late Quaternary is complex. Glacigenic debris flows (GDFs) are sourced from a common and homogeneous part of the upper fan and only develop as coherent individual flows after downslope transport. Their genesis and mode of deposition mean that GDFs are confined to particular areas of trough-mouth fans; accumulation of these subglacial sediments is controlled by a combination of margin glaciology and fan morphology. Although most of the fan sediment is deposited as GDFs, during glacials considerable areas of trough-mouth fans are dominated by sedimentation of suspension deposits, associated with extensive meltwater release from a warm-based ice sheet and probable contour current activity. The depositional sequence of these two sediment types may be important in generating the long run-out distances of GDFs, which are initiated and sustained over low gradients. Furthermore, emplacement of GDFs is interpreted to be a relatively low-frequency event, and temporally, at least, fans are not dominated by this mode of sediment emplacement whilst ice sheets are at the shelf break. Large-scale trough-mouth fan development is therefore asynchronous and non-uniform, a result of the interaction between glaciology, morphology, and oceanography.
Experimental constraints on shear mixing rates and processes: implications for the dilution of submarine debris flows
Authors: Talling P. J. , Peakall J. , Sparks R. S. J. , Ó Cofaigh C. , Dowdeswell J. A. , Felix M. , Wynn R. B. , Baas J. H. , Hogg A. J. , Masson D. G. , Taylor J. , Weaver P. P. E. 
Published: April 2008

Abstract

Submarine debris flows show highly variable mixing behaviour. Glacigenic debris flows travel hundreds of kilometres along the sea floor without undergoing significant dilution. However, in other locations, submarine slope failures may transform into turbidity currents before exiting the continental slope. Rates and processes of mixing have not been measured directly in submarine flow events. Our present understanding of these rates and processes is based on experimental and theoretical constraints. Significant experimental and theoretical work has been completed in recent years to constrain rates of shear mixing between static layers of sediment and overlying turbulent flows of water. This work was driven by a need to predict transport of fluid mud and the erosion of cohesive mud beds in shallow water settings such as estuaries, docks and shipping channels. These experimental measurements show that the critical shear stress necessary to initiate shear mixing (around 0.1 to 2 Pa) is typically several orders of magnitude lower than the yield strength of the debris. Shear mixing should initiate at relatively low velocities (about 10–200 cm s
−1
) on the upper surface of a submarine debris flow, at even lower velocities at its head (about 1–10 cm s
−1
), and play an important role in mixing over-ridden water into the debris flow. Addition of small amounts of mud (approximately 3% kaolin) to a sand bed dramatically reduces the rate of mixing at its boundary, and changes the processes by which sediment is removed. Estimates are presented for rates of shear mixing at a given flow velocity, and for the critical velocity necessary for hydroplaning or a transition from laminar to turbulent flow. Although these estimates are crude, and highlight the need for further experimental work, they illustrate the potential for highly variable mixing behaviour in submarine flow events.
Late Pleistocene glacially-influenced deep-marine sedimentation off NW Britain: implications for the rock record
Authors: Davison Stephen , Stoker Martyn S. 
Published: April 2008

Abstract
A new deep-water borehole at the foot of the West Shetland Slope revealed a sequence of Late Pleistocene glacimarine sediments. This section comprises an interbedded sequence of muddy diamictons, with subordinate sandy muds with dropstones and matrix-poor sands and gravels. Integration of core data, seabed imagery and high-resolution seismic-reflection records indicate the succession is dominated by stacked glacigenic debris flows.
Individual debris flows are composed of massive, clast-poor muddy diamicton, and are seperated by sandy muds and the sands and gravels. The mud units are interpreted as a combination of hemipelagic-glacimarine and distal ice-rafted deposits. The sands and gravels are interpreted as the result of bottom-current reworking of glacial and pre-glacial sediments. The new data support previous studies which suggest that Pleistocene ice sheets reached the edge of the West Shetland Shelf on several occasions, delivering large volumes of glacigenic sediment directly to the shelf edge and upper slope. These deposits became unstable, forming debris flows which transported the glacigenic sediments to the deep-water environment. Seabed imagery shows that the area around the borehole formed a focus for this style of deposition.
A depositional model constructed from the new data is enhanced by the application of data from an ancient deep-water, glacially-influenced, succession from the Neoproterozoic Macduff Formation NE Scotland.
A glacial sequence stratigraphic model for temperate, glaciated continental shelves
Authors: Powell Ross D. , Cooper James M. 
Published: April 2008

Abstract
Temperate, glaciated continental shelves are by nature complex basins in that they not only have typical low-latitude siliciclastic processes acting to produce a sedimentary record and depositional architecture, but they also have the consequences of glacial action superimposed. For these settings glacial systems tracts are defined and related to glacial advance and retreat signatures, which can then be evaluated relative to changes in other external forces. We define glacial maximum (GMaST), retreat (GRST), minimum (GMiST) and advance (GAST) systems tracts separated by bounding discon-formities, which are respectively, the grounding-line retreat surface (GRS), the maximum (glacial) retreat surface (MRS) and the glacial advance surface (GAS). Each glacial advance and retreat sequence is bounded by a regionally significant unconformity, a glacial erosion surface (GES), or its equivalent conformity. Parasequence motifs vary across the shelf but include facies dominated by the movement of grounding lines. Facies motifs may have subglacial till above a GES and this is the main facies of the GMaST; however, tills are commonly absent. Although diamictic debrites are often associated with groundingline deposystems, the GRST succession is dominated by sorted deposits of gravel, rubble and poorly sorted sands due to the dominance of glacial meltwater. These deposits commonly have the geometry of banks or wedges/fans. They form the offlap-break at the outer continental shelf and also form a retrogradational stacking of bank systems on the shelf. Banks are capped by glacimarine rhythmites including thin debrites, turbidites, cyclopsams and cyclopels and perhaps iceberg-rafted varvites in fan to sheet-like geometries. Above these are draped sheets of bergstone muds that grade into paraglacial muds. The GMiST occurs with glacial retreat onto land or into fjords. The GMiST is represented in nearshore areas by progradational deposits of paralic systems dominated by deltaic and siliciclastic shelf systems, and in offshore areas by condensed sections. The GAST is represented by the inverse of the GRST facies succession, but is also the most likely interval to be eroded during readvance.
Geomorphology of buried glacigenic horizons in the Barents Sea from three-dimensional seismic data
Authors: Rafaelsen B. , Andreassen K. , Kuilman L. W. , Lebesbye E. , Hogstad K. , Midtbø M. 
Published: April 2008

Abstract
The glacigenic sequence of the southwestern Barents Sea shelf has for the first time been studied using 3-D seismic data. The close spacing of 3-D lines and powerful computer workstation interpretation techniques have allowed detailed mapping of the observed features. Several generations of subglacial lineations observed on four different palaeo-surfaces are interpreted to reflect the flow patterns of palaeo-ice sheets. To our knowledge, this is the first time that multiple levels of subglacial lineations have been observed. The lineations are 2.5–8 m in relief, 50 to 180 m wide and 0.5 to 20 km long. All four surfaces show a main lineation pattern comprising lineations with a N-S trend, suggesting that the dominant ice flow was directed northwards across the Barents Sea shelf at least four times during the last 0.8 Ma. Two of the surfaces display semi-circular to oblong depressions trending mainly in the same direction as the sub-parallel lineations. These depressions are 9–53 m in relief, 1.25–3.2 km wide and 1.9–9 km long. In contrast to the buried surfaces, the sea floor is dominated by 2.5–25 m deep cross-cutting iceberg plough-marks from the deglaciation phase of the last Barents Sea ice sheet. The 3-D seismic data are conventional industry data. Despite relatively low seismic frequencies and, hence, limited vertical resolution of seismic profiles, time slices and sub-horizontal time maps are of high spatial resolution, providing detailed images of different stages of buried Quaternary glacial geomorphology.
Millennial and sub-millennial-scale variability in sediment colour from the Barra Fan, NW Scotland: implications for British ice sheet dynamics
Authors: Wilson Lindsay J. , Austin William E. N. 
Published: April 2008

Abstract

Sediment colour, together with other proxy data, provides a novel, rapid and non-destructive tool in the investigation of glacier-influenced sedimentation on the Barra Fan, NW Scotland. Lightness (
L
*) and reflectance (400–700 nm) measurements at this site provide a quantitative estimate of changes in calcium carbonate and clay content. Interstadials are carbonate-rich/clay-poor (higher
L
* and reflectivity), whereas stadials are carbonate-poor/clay-rich (lower
L
* and reflectivity). Detailed sedimentological investigations suggest that the last British Ice Sheet (BIS) extended to the outer continental shelfbreak shortly after 30 ka
bp
. This climatic response of the BIS to global cooling at the Marine Isotope Stage (MIS) 3 – 2 transition marks a significant increase in sediment delivery to the Barra Fan. Prior to 30 ka
bp
, strong Dansgaard/Oeschger (D/O) cyclicity dominates the record. After 30 ka
bp
, shorter periodicities prevailed as the BIS reached its maximum extent. Glacier dynamics plays a significant role in the delivery of ice-rafted debris (IRD) across this margin, highlighting the inherent difficulties of correlating millennial-scale IRD events when the IRD is derived from different ice sheets. An event stratigraphy based upon carbonate-rich interstadials provides a more robust means of amphi-Atlantic correlation during this interval.
Observations of surge periodicity in East Greenland using molybdenum records from marine sediment cores
Authors: Woodward John , Carver Steve , Kunzendorf Helmar , Bennike Ole 
Published: April 2008

Abstract

This paper describes a unique record of glacier flow instability for East Greenland during the Little Ice Age. Trace metal analysis of sediment cores collected during 1998 from the Noret Inlet in the Mesters Vig area of East Greenland shows two peaks in the molybdenum (Mo) record at 495 ± 40 years
bp
and 95 ± 2 years
bp
. This is notable as there is no molybdenum mineralization in the geology of the Noret Inlet catchment area. Molybdenum is found, however, in the drainage basin of Mesters Vig Inlet, just to the south of the Noret Inlet. The molybdenum record in the Noret core provides a long-term surge record for the Östre Gletscher, a large surge-type glacier in the Werner Bjerge that drains into Mesters Vig Inlet. The two molybdenum peaks indicate surge termination for the glacier, indicating a surge recurrence interval of around 400 years.
Timing and tectonic controls in the evolving orogen of SE Asia and the western Pacific and some implications for ore generation
Authors: Macpherson Colin G. , Hall Robert 
Published: April 2008

Abstract
SE Asia lies at the convergence of the Eurasian, Pacific and Australian plates. The region is made up of many active arcs, extensional basins, and the remnants of similar tectonic environments developed throughout the Cenozoic. There are many important hydrothermal mineral deposits and prospects in SE Asia but their formation is often poorly understood due to the complicated tectonic history of this region and the knowledge of relationships between mineralization and tectonics. Plate reconstruction offers a framework to integrate geological and geochemical data that can be used to unravel the large-scale tectonic processes that affected mineralized provinces. We present examples of the information that can be derived from this approach and discuss the implications for understanding the origin of some hydrothermal mineral deposits in SE Asia.
Example of a structurally controlled copper deposit from the Hercynian western High Atlas (Morocco): the High Seksaoua mining district
Authors: Chauvet A. , Barbanson L. , Gaouzi A. , Badra L. , Touray J. C. , Oukarou S. 
Published: April 2008

Abstract

The mineralized district of the High Seksaoua (Western High Atlas, Morocco) is characterized by a lithological succession marked by an alternation of schists and limestones attributed to the Cambrian and affected by at least five deformational events. The copper mineralization herein analysed is systematically localized close to a dolomite/black schist level in which a top-to-the-NNW décollement-type tectonics (D
d
) has been identified. We demonstrate that the economic mineralization is a syn-tectonic stockwork formed in response of this top-to-the-NNW shearing event (D
d
). This tectonic event can be reasonably correlated with the late Hercynian tectonics responsible, in the same area, for the Tichka granite emplacement at
c.
291 ± 5 Ma, also under the control of a NW-SE shortening direction. Indeed, the Tichka granite represents a good candidate to explain the origin of the mineralized fluid. Such an hypothesis is confirmed by the Permo-Triassic age (
c.
270 Ma) given by
40
Ar/
39
Ar dating realized on white micas related to the stockwork formation (this study). This important result questions the syn-genetic interpretation accepted until now for this mineralization and allows us to propose a new model of formation for this kind of deposit that could contribute to exploration programmes.
Indo-Antarctic Correlation: a perspective from the Eastern Ghats Granulite Belt, India
Authors: Dasgupta Somnath , Sengupta Pulak 
Published: April 2008

AbstractAvailable lithological, petrological and geochronological data on the rocks of the Eastern Ghats Belt (EGB), which has a key role to play in any model of Indo-Antarctic correlation in Precambrian and Cambrian times, have been synthesized and interpreted. Longitudinal lithological subdivisions of the belt are mostly not supported by recent geochronological data, which rather suggest a fourfold division based on protolith ages of the ortho- and paragneisses. Mineral ages show prominent tectonothermal events at Mesoproterozoic, Grenvillian and Pan-African times. However, not all of the imprints of all the events are preserved in all the geochronological domains. In the most well-studied Domain II, three phases of metamorphism are recorded — an early ultra high-temperature metamorphism with an anticlockwiseP-Tpath, a second granulite facies event atc.1000 Ma, with a retrograde trajectory of near-isothermal decompression, and a third of amphibolite facies. The available information, however, is not conclusive as to whether or not the entire EGB experienced polyphase UHT metamorphism. The propagation of the Grenvillian orogenic front in the EGB is identified.
Crustal architecture and evolution of the Eastern Ghats Belt and adjacent regions of India
Authors: Dobmeier Christoph J. , Raith Michael M. 
Published: April 2008

AbstractExtending along the east coast of peninsular India, the Eastern Ghats expose a deep section through a composite orogenic belt that once formed part of the Proterozoic mobile belt system within East Antarctica and East India. The critical evaluation of the existing geological and isotopic data strongly suggests that this orogenic belt includes not only the granulite facies Eastern Ghats Belt but also the Nellore-Khammam Schist Belt and lower grade units at the southern margin of the Singhbhum Craton. The present authors propose its subdivision into four crustal provinces with widely different geological evolutions. The Rengali and Jeypore Provinces formed at the margin of the Bhandara Craton in the Late-Archaean. In the Krishna Province, volcanosedimentary rocks equivalent to the Cuddapah Supergroup accumulated, probably on the Dharwar Craton in the Palaeoproterozoic, and the major tectonometamorphic event took place between 1.67 and 1.55 Ga, subsequent to a short-lived igneous activity. The Eastern Ghats Province, which shows considerable similarities with the Rayner Province of East Antarctica, was strongly affected by pervasive deformation, high-grade metamorphism and crustal-derived magmatism between 1.1 and 0.9 Ga, which extensively modified the crustal structure of present eastern peninsular India. Neoproterozoic and Early Phanerozoic tectonothermal activities were largely restricted to pre-existing shear zones, but the present configuration of the composite orogenic belt may have been achieved only during the Pan-African Orogeny.
Proterozoic crustal evolution of southernmost India and Sri Lanka
Authors: Braun Ingo , Kriegsman Leo M. 
Published: April 2008

AbstractThe Southern Granulite Terrain of India comprises four Proterozoic domains (from north to south): the Madurai Block, and the Achankovil, Ponmudi and Nagercoil Units. All but the Achankovil Unit share similarities with the Highland Complex of Sri Lanka: (1) evidence for Palaeoproterozoic crust formation (from U-Pb ages and 2.0–3.0 Ga Nd model ages); and (2) Pan-African ultrahigh-temperature metamorphism between 610 and 550 Ma. More specifically, the Ponmudi Unit and the Madurai Block share lithological and petrological characteristics with the low-Pand high-Pdomains of the Highland Complex, respectively. The Achankovil Unit is correlated with the Wanni Complex of Sri Lanka on the basis of lithologies and Nd model ages (1.0–2.0Ga). These domains and the Vijayan and Kadugannawa Complexes of Sri Lanka represent Late Mesoproterozoic-Early Neoproterozoic crustal domains.Similarities in tectonic style, degree of metamorphism and Neoproterozoic U-Pb ages, suggest a common Pan-African tectonothermal evolution for the lower crustal domains of southern India, Sri Lanka and the Lützow-Holm Bay of Eastern Antarctica. Sri Lanka may have been located at the junction between the Mozambique Belt and a second belt partly involving areas that underwent a Grenvillian high-grade event during the formation of Rodinia. Madagascar shows a similar Pan-African metamorphic overprint, but is located in a different position and lacks the influence of the second belt. Alternative views are discussed.