bluuebunny/crossref_metadata_2025_split huggingface dataset:
Major river systems of central and southern Britain during the Early and Middle Pleistocene
Authors: Rose J. 
Published: July 2007

ABSTRACTCentral and southern Britain was drained by two main river systems during the larger part of the Early and Middle Pleistocene: the Thames and Bytham rivers. Evidence for these rivers and their Quaternary history is represented by their sediments (the Kesgrave and Bytham Sands and Gravels, respectively), the geomorphological position of the sediments, biostratigraphy and amino acid geochronology. Evidence from the earlier parts of the Early Pleistocene (Tiglian C4b and earlier) indicates low‐energy river systems and marine conditions over much of East Anglia. For most of the Early Pleistocene (Tiglian C4c to the Cromerian Complex) the ancestral Thames was the main river with, at its maximal extent, a catchment that extended into Wales, and across East Anglia and what is now the North Sea, to join the ancestral Rhine. During this period, glaciers in the uplands of Wales and periglacial mass movement elsewhere supplied material to the catchment and it was at this time that the bulk of the sorted Quaternary ssediments of lowland Britain were deposited. The Bytham river system has no successor because the landscape now in existence has been fundamentally altered by glacial erosion. This catchment drained most of Midland England and joined the Thames in central East Anglia. Initially, the Bytham river was a tributary of the Thames, but over time it extended its catchment and at the beginning of the ‘Cromerian Complex’it became the main river of southern Britain. With the Anglian Glaciation (01 Stage 121, the Bytham river was destroyed and the Thames was diverted to its present route through London.
The Somme valley terrace system (northern France); a model of river response to Quaternary climatic variations since 800,000 bp
Authors: Antoine Pierre 
Published: July 2007

ABSTRACTRecent research on the Somme Valley terrace deposits, that began in 1987, has resulted in an integrated sequence of geological and geomorphological evidence for this area that is of particular significance for prehistoric investigations. This has been achieved using previous evidence and new results from archaeological and geological excavations. These include longitudinal profiles, cartography and detailed synthesis of sections of alluvial deposits, stratigraphy of river deposits and overlying loess sequences. The work, based on a study of the geometry of the terrace system, has resulted in the identification of ninestepped alluvial formations that occur along 70 km of the valley. Detailed study permits the integration of the various alluvial sequences. This suggests that each alluvial sequence results from sedimentation through a single glacial‐interglacial climatic cycle. This hypothesis is confirmed by investigation of soil and loess sequences of the deposits overlying the fluvial sediments. The synthesis presented provides a basis for understanding the deposition of the terrace system and an initial chronostratigraphic interpretation for the deposits.
Quaternary evolution of a meandering gravel bed river in central Spain
Authors: Alonso A. , Garzón G. 
Published: July 2007

ABSTRACTThe river Jarama is a medium‐sinuosity meandering river with gravel bedload. Throughout the Quaternary it developed a large number of terraces in a repetitive sequence of aggradation‐stability‐degradation‐stability stages, which are studied in the middle reach of the river, applying geomorphological and sedimentological methods, as well as kadiocarbon dating techniques. The Upper Terrace System of earliest Pleistocene to mid Pleistocene age forms isolated fragments vertically disconnected and colluviated, and their sequential distribution of facies implies lateral shifting of channels and a welldeveloped flood plain. The Middle Terrace System of mid‐to‐late Pleistocene age has differentiated levels in the upstream reaches while downstream they condense giving a thick multi‐episodic series, corresponding to the tectonic tilting of the basin. Classical point bar fining‐upward sequences of a medium‐ to high‐sinuosity river (with gravels and sands as bedload) are clearly differentiated in them. A major degradation stage follows this group of terraces, with an incision of up to 30 m. Then, during a relatively long period of stability, a forest of riparian species developed, prior to the last aggradational stage of the Lower Terrace System. The aggradation resulted in a fining‐upward sequence where lateral accretion is clearly visible in the gravels, due to migration of the medium‐ to low‐sinuosity river. Sedimentation continued and was active up to the 1950s, but since then, intense anthropogenic modifications led to renewed incision of the river.
Climate‐related river activity at the Weichselian‐Holocene transition: a comparative study of the Warta and Maas rivers
Authors: Vandenberghe J. , Kasse C. , Bohncke S. , Kozarski S. 
Published: July 2007

ABSTRACTHuvial systems from the Dutch and Polish lowlands are compared for their evolution during the Weichselian deglaciation period. In both regions the Pleniglacial braided‐river pattern changed to a meandering pattern in the beginning of the Lateglacial. Several transitional stages between braided and high‐sinuosity meandering systems have been recognized. A difference in fluvial activity is found during the Younger Dryas when the Maas transformed to a braided pattern while the Warta maintained its meandering pattern. Phases of erosion and aggradation are more or less synchronous in the different river basins, but their intensity may differ greatly. The major characteristics of the fluvial systems are obviously a response to the general climatic evolution and related to changes in vegetation. The regional differences are of minor importance and can be explained by site‐specific factors. Threshold values within the latter factors define the changes in river dynamics.
Reflection of the glacial‐interglacial cycle in the evolution of the Vistula river Basin, Poland
Authors: Starkel Leszek 
Published: July 2007

ABSTRACTA variety of factors has controlled the evolution of the Vistula river valley. They include climatically induced changes of the river runoff and sediment load, glacial advances and rapid variations of the base level, as well as the influence of the tectonic factor. The first‐order climatic cycles are reflected in separate terrace fills. The second‐order fluctuations may be represented by separate cuts and fills, by the change of the facies or by the change in the granulometric composition. The analysis of the changes in the longitudinal profile helped to discover a great variety of different valley reaches and a general tendency to smooth the long profile during the Quaternary.
Pleistocene evolution of the Danube in the Carpathian Basin
Authors: Gábris Gyula 
Published: July 2007

ABSTRACTThe present‐day drainage system of the Carpathian Basin originates from the gradual regression of the last marine transgression (brackish Pannonian Sea). The flow directions of the rivers including the Danube, are determined by the varying rates and locations of subsidence within the region. The Danube, which forms the main axis of the drainage network, first filled the depression of the Little Plain Lake and then, further southward, the Slavonian Lake. From the end of the Pliocene, the crustal movements which caused the uplift of the Transdanubian Mountains, forced the Danube to flow in an easterly direction, towards the antecedent Visegrid Gorge, and into the subsiding basins of the Great Plain. Climatic changes during the Pleistocene had the effect of forming up to seven fluvial terraces. The uplift of the mountains is demonstrated by the deformation of the terraces, while the subsidence of the Plains is proven by an accumulation of several hundred metres of sediment. The river only occupied its present position south of Budapest in the latest Pleistocene.
Morphology and post‐Chaudian (Late Pleistocene) evolution of the submarine Danube fan complex
Authors: Wong H.K. , Panin N. , Dinu C. , Georgescu P. , Rahn C. 
Published: July 2007

ABSTRACTThe Danube deep sea fan in the northwestem Black Sea has a lateral dimension of over 150 km and stretches from several hundred metres water depth down to the abyssal plain. Eight seismic sequences have been recognized in the fan complex. Each sequence consists of channel, levee and overbank deposits, as well as mass transport units. The Danube and the Ukrainian rivers have aggraded two surficial channel‐levee systems which diverge and decrease in volume downfan. The channels of these systems have a low sinuosity, implying young age, steep gradients and/or limited sediment supply. Significant channel migration occurred in the course of fan development, which could be largely controlled by relative sea‐level changes. The six youngest sequences mapped have been correlated to sea‐level fluctuations from the post‐Chaudian regression to the present day.
Imaging of the Moho depth in Madagascar through the inversion of gravity data: geodynamic implications
Authors: Fourno Jean‐Pierre , Roussel Jacques 
Published: July 2007

ABSTRACTSeveral E‐W profiles of Bouguer anomalies across the Precambrian basement were inverted by applying a linearized inversion procedure in the spectral domain and using a simplified two‐layer model with a crust‐upper mantle interface of constant density contrast. From these inverted profiles, a contour map of Moho topography has been constructed which covers the area of exposed Precambrian basement in the eastern and central parts of the island. Such imaging of the Moho depth in particular exhibits a N20°E‐trending zone of substantially thinned crust along the axis of the island. This parallels the east coast margin which resulted from the northward motion of India relative to Madagascar in the Upper Cretaceous. From combined analysis of geological, tectonic and metamorphic observations, this prominent crustal feature in the Precambrian basement of Madagascar is interpreted as the relic of continental lithospheric extension and thinning possibly related to Panafrican collapse tectonics on the eastern edge of the Mozambique belt. This extensional feature would have been reactivated only in part during the rifting and dislocation stages of the Madagascar and India continental blocks as evidenced by an axis of Cretaceous volcanism emphasized by the Ankaratra and Itasy massifs. Final separation nevertheless occurred further east, at the site of the east coast margin.
Neogene carbonate stratigraphy of Ontong Java Plateau (Western Equatorial Pacific): three unexpected findings
Authors: Berger W.H. , Stax R. 
Published: July 2007

ABSTRACTThe Neogene carbonate stratigraphy of five sites drilled on Ontong Java Plateau during Leg 130 reveals a number of patterns which are unexpected, and which we refer to as loss paradox, equatorial insensitivity, and climate paradox. They denote the following unresolved questions.

The loss of carbonate at depth (as derived from differences in accumulation rates) is much greater than suggested by the change in carbonate percentages (calculated under the assumption that carbonate dissolution is the cause of loss). This indicates an important role for redeposition processes, such as winnowing (bottom currents), sifting (resuspension and catabatic flow) and episodic sloughing or solifluction (presumably stimulated by earthquakes).
Accumulation rates are not markedly increased at the time a site crosses the equator. There are several possible reasons. Equatorial upwelling may be unimportant in controlling sedimentation rates this far in the western Pacific, or its output may be spread over a considerable distance from the equator. Alternatively, increased supply below the equator is compensated for by increased removal (e.g. from resuspension by bioturbation, combined with catabatic flow). It is conceivable that errors in the timescale could also produce the effect seen.
There is an overall tendency for agreement between the stratigraphic patterns of carbonate content and of accumulation rates, but neither pattern is readily explained by reference to changes in climate (represented by benthic δ18O) or in sea‐level (as derived from sequence stratigraphy).
Local displacement rate cycles in the life of a fold‐thrust belt
Authors: Butler Robert W.H. , Bowler Sue 
Published: July 2007

ABSTRACTThe evolution of minor structures during the growth of major folds and thrusts, in the Chartreuse district of the French Subalpine thrust belt, shows that each thrust evolved through a phase of distributed faulting, major thrust propagation and displacement, followed by distributed shear modification of the hanging‐wall fold. Microstructural studies suggest that the distributed faulting phases, early and late in the history, were characterized by strain rates limited by diffusive mass transfer processes (c. 10‐15‐10‐16 s‐1). Faulting whose rate is limited by DMT is too slow on its own to accommodate the regional time‐averaged shortening rates for the thrust belt as a whole, implying that the slow thrusts operated in tandem with those major, fast thrusts where deformation was primarily cataclastic. Consequently each thrust anticline experienced a displacement rate cycle and an array of thrust anticlines must amplify simultaneously. These interpretations raise important issues for the dynamics of fault populations, the evolution of thrust wedges and the history of fluid migration in thrust belts.
The Kolmogorov model of bed‐thickness distribution: an assessment based on numerical simulation and field‐data analysis
Authors: Muto Tetsuji 
Published: July 2007

ABSTRACTKolmogorov's model of the distribution of bed thicknesses is assessed by numerical simulations of a sedimentation process, assumed to be a random time‐series of alternating depositional and erosional episodes conformable with a stationary Markov process in a state of equilibrium. The study supports the validity of the main point of the model. The random time‐series process generates a succession of beds with ‘positive’ (preserved) and ‘negative’ (eroded) thicknesses, the frequency distribution of which, f(x), spans the range of positive to negative x‐values. The beds with negative thicknesses are absent in the stratigraphic record, whereby the measured bed thicknesses show a frequency distribution, f*(x | x > 0), that is left‐side truncated, cut off at the zero thickness value. The numerical simulations further indicate that f(x) is a ‘composite’ geometrical distribution, whose actual form changes progressively with pd, the probability of sediment deposition relative to erosion. The distribution f(x) invariably has a maximum at x≤0, such that the truncated distribution f*(x) for pd≥0.5 is a simple geometrical distribution regardless of pd value. The f*(x) distribution will appear to be a negative exponential distribution when based on the bed‐thickness data measured in a conventional metric scale. Data sets from four different turbidite successions in the Cenozoic of Japan, each comprising a few thousand beds, show this type of distribution. However, the sandstone‐capping shales in one of the turbidite successions show a truncated Gaussian distribution, attributed to a significant component of non‐turbiditic mud. No universal form of bed‐thickness distribution can be assumed for the Kolmogorov model. The form of bed‐thickness distribution may vary with the type of the depositional process and the character of the sedimentary environment.
When did Sardinia stop rotating? New palaeomagnetic results
Authors: Vigliotti L. , Langenheim V.E. 
Published: July 2007

ABSTRACTPrevious palaeomagnetic results from Tertiary volcanic rocks of Sardinia suggest that the island underwent a quick counterclockwise rotation between 20.5 and 19 Ma. In order to test this hypothesis, a new palaeomagnetic study was carried out on sediments and volcanic rocks with well‐controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation.Unrotated palaeomagnetic directions obtained from the Upper Ignimbrites (radiometric age: 18.5–19.7 Myr) and the Aquitanian tuffs collected in the Anglona region (N Sardinia) would suggest that the rotation ended earlier than 20.5 Myr. The directions found in the volcanics are perhaps the result of secular variation, rather than differential rotation of the Anglona region with respect to surrounding regions.Two sites belonging to the upper ignimbritic unit (SI2) in the Monte Traessu‐Monte Rispisu area (Logudoro region) exhibited a large amount of rotation (D=320.4°, I=60°) which may be age related (radiometric age: 19.9 Myr). Four dikes (radiometric age: 18.3–16.7 Myr) in the Arcuentu volcanic complex (Arburese region) yield results (D=348.4°, I=33.8°) that indicate a further amount of rotation after their emplacement.Stable end‐point directions were successfully isolated from three Upper Burdigalian/Langhian sedimentary sites (biostratigraphic age: 18–15Ma) from the Marmilla and Logudoro regions. Consistent paleomagnetic directions obtained from these sites (D=352°, I=49°) indicate that a small amount of rotation was still to be completed in the Langhian time. This result is consistent with the history of Sardinian volcanism, which did not end until 13 Ma.
Oblique rifting in Salina, Lipari and Vulcano islands (Aeolian islands, southern Italy)
Authors: Mazzuoli Roberto , Tortorici Luigi , Ventura Guido 
Published: July 2007

ABSTRACTA structural analysis carried out on the volcanic products of the islands of Salina, Lipari and Vulcano (Aeolian archipelago) points out that the large‐scale tectonic setting is dominated by NW‐SE trending right‐lateral extensional strike‐slip faults and by N‐S to NE‐SW trending normal faults and fractures. This fault pattern generates pull‐apart type structures, developing between different right‐hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike‐slip faults. All the structures, representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands, are kinematically compatible with a N100°E extension related to a rifting process affecting southern Italy.
Fluid venting from a mud volcano in the Mediterranean Ridge Diapiric Belt
Authors: Cita M.B. , Woodside J.M. , Ivanov M.K. , Kidd R.B. , Limonov A.F. ,   Scientific Staff of Cruise TTR3 ‐ Leg 2
Published: July 2007

ABSTRACTDirect observation of active emission of fluids and mud from a submarine mud volcano were made for the first time in an extensive field of mud diapirs and mud volcanoes on the Mediterranean Ridge using a video camera towed 2 m above the seafloor in 1800 m of water. This recent research using both long range and deep‐towed sidescan sonar systems indicates also that diapirism and eruption of mud along the crest of the ridge is more common than previously thought. The southwards increase in age of rock fragments carried within the erupted mud supports the hypothesis that the fluid mud becomes overpressured within a southward‐dipping backthrust from the Inner Deformation Front of this accretionary prism.
Representation of normal slant faults in a 2D burial history model
Authors: Lerche I. , Yu Z. , Liu J. 
Published: July 2007

ABSTRACTA discussion is given of the impact of normal slant faults on basinal structure, compaction, fluid overpressure development, and thermal effects in sedimentary basins. Faults which are hydraulically closed or open to fluid flow are examined in a dynamical two‐dimensional fluid/ flow compaction model.From this numerical investigation three dominant factors characterize the effects of single and multiple faults with open or closed hydraulic behaviours: (i) there is a difference in excess pressure for fault planes with open or shut hydraulic conditions, but the neighbourhood where the effect of the fault is dominant is fairly localized (to within about half a kilometre or so laterally from the fault plane); (ii) the lateral and vertical motion of sediments between faulted blocks induces a thermal difference prior to, during, and post‐faulting, which can play a role in influencing hydrocarbon generation, migration, and accumulation; (iii) porosity retention and permeability modification by fault development could influence hydrocarbon exploration decisions regarding sealing, migration pathways, and fluid retention.The general patterns of slant fault effects described here should prevail in most geological situations, because the numerical experiments are designed to illuminate sharply the dominant response characteristics within the framework of simplified situations.
Sr isotope evolution of Maastrichtian seawater, determined from the chalk of Hemmoor, NW Germany
Authors: McLaughlin Ó.M. , McArthur J.M. , Thirlwall M.F. , Howarth R. , Burnett J. , Gale A.S. , Kennedy W.J. 
Published: July 2007

ABSTRACTIn 140 metres of Maastrichtian White Chalk (nannofossil chalk) exposed near Hemmoor, NW Germany, values of 87Sr/86Sr increase from 0.707760 in the Belemnella sumensis Zone (Lower Maastrichtian) at the base of the section (‐54.5 m; referred to 0 m at a prominent marl, M900) to 0.707821 in the Belemnella baltica/danica Zone (Upper Maastrichtian) at the top of the section (+84.5 m). A plateau in 87Sr/86Sr occurs between ‐5m and +50m in the section, probably as a result of a very high rate of sedimentation in this interval. A belemnite and associated nannofossil chalk have similar 87Sr/86Sr values, suggesting that there has been little diagenetic alteration of the 87Sr/86Sr ratios in the chalk, which therefore preserves its original 87Sr/86Sr. Comparison of 87Sr/86Sr and nannofossil zonations for sequences at Bidart, France, and DSDP Sites reveals discordance and so possible diachronism of the basal boundaries of nannofossil Zones CC25B and CC25C.
A new indicator of movement direction during orogenesis: measurement technique and application to the Alps
Authors: Bell T.H. , Forde A. , Wang J. 
Published: July 2007

ABSTRACTThe orientation of axes of sigmoidal, staircase or spiral inclusion trails within porphyroblasts provides an indicator of the direction of movement during deformation that is synchronous with metamorphism. A simple technique is presented in detail to find this axis in 3D by radially sectioning a horizontal slab cut from an oriented sample. When viewed from one direction, the switch in asymmetry of the porphyroblast inclusion trails in these sections defines the trend of the axis. Further radial sectioning of a vertical slab cut parallel to this trend determines the plunge of this axis.This technique is independent of the model adopted for the formation of sigmoidal or spiral‐shaped inclusion trails and can be used to evaluate the mechanism by which they form. It can also be used to evaluate theories of folding and orogenesis. Measurements of spiral and sigmoid axes in garnet porphyroblasts from the European Alps show that they reflect the movement of the African Plate relative to Europe better than linear indicators preserved within the same rocks.