bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequence and systems tract interpretation of the epicontinental Oligocene deposits in the Danish North Sea
Authors: Michelsen O. , Danielsen M. 
Published: September 2007

Abstract
A sequence stratigraphical scheme has been established for the siliciclastic Cenozoic deposits in the southeastern North Sea Basin. The present paper addresses the problem of recognizing systems tracts by means of logs, using the Oligocene sequences as an example. The Oligocene sequences are characterized by an overall prograding seismic reflection pattern, and systems tracts cannot be interpreted from seismic sections alone.
The sequences are dominated by marine clay deposits, and abrupt changes in lithological facies are rarely seen. The gamma-ray log trends indicate retrograding, aggrading and prograding stacking patterns.
The lowstand deposits are identified as prograding sedimentary bodies. Coarse-grained sharp-based lowstand deposits are found basinwards of the depositional shoreline break of the preceding sequence, and further basinwards they are more fine-grained. Fan deposits are not recognized. A thin interval of transgressive deposits including upward fining clayey sediments is found at the top of the lowstand deposits and in the landward direction at the top of the older highstand deposits. The maximum flooding surface is identified by a high gamma-ray peak. The overlying highstand deposits thicken in the landward direction, and are here characterized by an upward coarsening trend. They thin in the basinward direction and become a condensed clay interval.
Deposition took place during a tectonically quiet period in an epicontinental basin with a gently southwestward dipping sea floor. The lowstand deposits comprise forced regressive deposits and prograding deposits, and a deep ramp model is, therefore, suggested for these deposits.
Sequence stratigraphy and architecture on a ramp-type continental shelf: the Belgian Palaeogene
Authors: Jacobs P. , De Batist M. 
Published: September 2007

Abstract
In Palaeogene times, the ‘Southern Bight’ of the North Sea functioned as an intracratonic, shallow-marine, siliciclastic basin and accumulated a few hundred metres of gently dipping sediment packages. A fine-scale seismic-stratigraphical model for the Palaeogene was formulated on the basis of a dense, high-resolution reflection seismic grid. In total 13 major seismic-stratigraphical units were defined, based on geometry and seismic facies characteristics. The seismic stratigraphy has been complemented with the results of four cored wells near the Belgian coast, containing a nearly continuous, 200 m thick sediment succession of Eocene age. Facies analyses of these cores suggest that part of these sediments were deposited on a muddy shelf and part in adelta environment. Evidence from relevant onshore outcrops has been used to complete the geological history of the Palaeogene, with special emphasis on the Eocene. A sedimentation model for the Eocene is presented, and relative sea-level changes, regional tectonic events and changes in sediment input are discussed. Genetic interpretation of the various lithological units and the large-scale architecture of the ramp-type margin enable evaluation of sequence-stratigraphical concepts, initially defined for a typical shelf-slope-basin section along an Atlantic-type continental margin.
Estuarine and shallow-marine sedimentation in the Upper Cretaceous-Lower Tertiary west-central Patagonian Basin (Argentina)
Authors: Spalletti L. A. 
Published: September 2007

Abstract
The Upper Cretaceous-Palaeocene Paso del Sapo-Lefipán Basin of west-central Patagonia (southern Argentina) is an intracratonic depocentre located to the east of the Andean magmatic arc. The depression is related to uplifted basement blocks and was generated by a complex system of strike-slip faults.
The sedimentary infill comprises two stratigraphical units: the Paso del Sapo and the Lefipán Formations. The Campanian-Maastrichtian Paso del Sapo Formation (145 m thick) is mainly composed of quartz-rich sandstones and conglomerates associated with minor heterolithic intervals, mudstones and coal beds. The Maastrichtian-Palaeocene Lefipán Formation (200 m thick) is composed in its lower part of gypsiferous mudstones and shales with isolated cross-bedded and plane-bedded sandstone bars. The middle and upper sections of this unit are distinguished by cross-bedded sandstone multi-storeys associated with several coquina beds.
Sediments from Paso del Sapo Formation show features of fluvial and tidally influenced systems. Sandstones and conglomerates were deposited as subtidal and intertidal estuarine bars. Heterolithic sections, mudstones and coal beds represent the more restricted inter- to supratidal marginal estuarine deposition.
Most of the Lefipán Formation was formed under open marine conditions. Offshore fine-grained transgressive deposits accumulated during basin starvation. Later on, sandstone multi-storeys and coquinas were deposited in a wave and tidally influenced lower to upper shoreface environment.
The sedimentary record of the K-T basin is in the range of a second-order eustatically controlled cycle. Based on facies arrangement and stratal geometries, the estuarine deposits of the Paso del Sapo Formation and the basal section of the Lefipán Formation are interpreted as a retrogradational systems tract. Later on, during a highstand period, the middle and upper Lefipán Formation was deposited as a progradational systems tract.
Quaternary siliciclastic sequence stratigraphy of western Mediterranean passive and tectonically active margins: the role of global versus local controlling factors
Authors: Ercilla G. , Alonso B. 
Published: September 2007

Abstract
A study of the Quaternary sequence stratigraphy of two siliciclastic Spanish Mediterranean margins with a different geological setting was carried out. This study reveals that the Quaternary stratigraphical architectures of the northern Catalonia passive continental margin and of the northwestern Alboran tectonically active margin are mainly characterized by the stacking of high-frequency lowstand systems tracts. Only the Versilian transgressive and Holocene highstand systems tracts have been recognized. This kind of stratigraphical architecture is the product of the eustatic cyclicity characterized by sea-level changes of high frequency, high amplitude and marked asymmetry, regardless of local geological context.
On the other hand, local factors seem to play an important role in the stratal pattern, its preservation and sedimentary distribution. Thus, tectonics was responsible for strong lateral variations in margin growth pattern, changing from progradational to divergent in the tectonically active margin of the northwestern Alboran. Tectonics also conditioned the preservation of the lowstand systems tracts along and through the margin: the lowstand systems tracts are preserved from shelf in subsiding areas, e.g. northern Catalonia and the central sector of the northwestern Alboran, and from slope in uplifting areas, e.g. eastern and western sectors of the northwestern Alboran. Physiography conditioned the across-margin location of sedimentary depocentres: on the outer shelf and upper slope, when the shelf is relatively wide as occurs in northern Catalonia, and on the base-of-slope when the shelf is relatively narrow as occurs in the northwestern Alboran. Variations in the volume of sediment supply conditioned the along-margin location of sedimentary depocentres, which changed from south to north in northern Catalonia.
Late Pleistocene-Holocene high-resolution sequence analysis on the Alboran Sea continental shelf
Authors: Hernández-Molina F. J. , Somoza L. , Rey J. 
Published: September 2007

Abstract

We present results of a detailed high-resolution seismic stratigraphy analysis of the northwestern margin of the Alboran Sea, between Málaga and the Gibraltar strait, based on a network of high- and very high-resolution seismic profiles. These profiles allow the determination of several scales of depositional sequences that are related to relative sea-level cycles of different order on the continental shelf and slope. The Late Pleistocene-Holocene deposits on these comprise ten seismic units characterizing lowstand, transgressive and highstand deposits. These deposits allow definition of a main Type 1 depositional sequence for the last 20 ka sedimentary record. This sequence is made up of minor depositional sequences produced by high-frequency relative sea-level cycles with a frequency range below the Milankovitch band. In this way, the last eustatic hemicycle was modulated by three types of very high-resolution sea-level cycles: The ‘P cycles’, being longest, caused the major sedimentary progradations (P
1
, P
2
, P
3
, P
4
and P
5
). The smaller eustatic changes of the ‘h cycles’ created smaller progradations, and the ‘c cycles’, consisting of short stillstands, resulted in sets of minor progradations within the larger cycles.
Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf
Authors: Correggiari A. , Field M. E. , Trincardi F. 
Published: September 2007

Abstract
The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form.
We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20–24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.
Seismic expression of depositional sequences associated with expansion and contraction of ice sheets on the northwestern Antarctic Peninsula continental shelf
Authors: Bart P. J. , Anderson J. B. 
Published: September 2007

Abstract
We present results from seismic stratigraphical analysis of a regional grid of intermediate-resolution seismic profiles from the Antarctic Peninsula continental shelf that reveal greater complexity in the stratigraphical record than has been previously recognized using lower-resolution seismic records. Widespread unconformities and prograding stratal patterns are interpreted as subglacial erosional surfaces and proglacial depositional systems respectively. Two types of units are recognized, aggrading-shelf units and prograding-slope units.
Aggrading-shelf units display minimal slope progradation (less than 2 to 3 km) beyond the pre-existing shelf edge. Units of this type are composed of either acoustically layered prograding foresets or acoustically chaotic seismic facies. Unit thicknesses vary along the shelf from less than 20 ms two-way travel time to more than 200 ms. Low-angle foresets downlap and partially fill palaeotroughs that were formed during prior glacial advances. Foresets are interpreted as proglacial depositional surfaces. The zones of active proglacial deposition were lobate in shape and ranged in width from a few kilometres to more than 30 km. Toplap truncations of foresets result from ice-sheet expansion over proglacial deposits.
Glacial erosion on the shelf was concentrated along the axes of ice streams to form deep troughs. Slope progradation occurred mainly near the mouths of these troughs. Prograding-slope units exhibit local slope progradation in excess of 2 to 3 km beyond the location of the pre-existing shelf edge.
Shifts in the position of troughs indicate lateral shifts in the positions of ice streams. Hence, sedimentation on the outer shelf and upper slope is point-sourced, not line-sourced, and individual units change from progradational to aggradational along the margin. It is not possible to interpret the ice-sheet grounding history of the shelf using changes in stratal stacking patterns without constraining these lateral changes. However, detailed mapping of prograding-slope units does reveal regional trends that imply glacial periods when greater quantities of sediment were eroded from the shelf and deposited on the slope. We interpret prograding-slope units as having been formed during relatively long-duration glacial expansions. Ice-sheet retreat from the shelf probably occurred rapidly, as indicated by a lack of backstepping proglacial deposits.
Quaternary erosion and depositional processes: western Norwegian fjords, Norwegian Channel and North Sea Fan
Authors: Sejrup H. P. , King E. L. , Aarseth I. , Haflidason H. , Elverhøi A. 
Published: September 2007

Abstract

The southern Norwegian fjords, the northern North Sea and North Sea margin represent major pathways of sediment flux from the southern part of Fennoscandia to the deep sea basin. Volumes, genesis and chronology of the temporary and semi-permanent Quaternary sediment repositories are reviewed. The fjord infill is dominated by sediments from the last deglaciation (150 km
3
). The Norwegian Channel is occupied by tills and glaciomarine/marine sediments (5000 km
3
). The North Sea Fan comprises glacially fed debris-flow fingers/lobes (constituting 80% of deposits in the mid- to late Pleistocene) together with hemipelagic and mass-transport slide sediments, totalling 15 000 km
3
. The Norwegian Channel represents a dynamic transport conduit whereby during peak glaciation a fast-flowing ice stream has drained large parts of the southern Fennoscandian ice sheet several times. The sediment flux to the deep sea is temporarily interrupted (between glacials) when stored in the channel but under glacial maxima the channel is probably largely bypassed, with material transported as subglacial load and deposited as debris flows on the North Sea Fan. Sediments on the fan have a much longer storage time (numerous glaciation cycles) but are further transported to the deep sea in large slide events. The volume of Quaternary sediments found along this sediment pathway, plus that which slid to the deep sea, total at least 25 000 km
3
, corresponding to an averaged 120 m of erosion across southern Norway.
The São Francisco strandplain: a paradigm for wave-dominated deltas?
Authors: Dominguez J. M. L. 
Published: September 2007

Abstract

The São Francisco ‘delta’ (total area 800 km
2
) has been considered for more than two decades as a paradigm for wave-dominated deltas. Although it is frequently cited in the literature, there is a paucity of published data about this sedimentary feature. At the time the modern models of deltaic sedimentation were proposed, many of those deltas receiving modifiers such as ‘wave-dominated’ and ‘tide-dominated’ were very poorly understood. Circularity of reasoning did the rest. Inevitably phenomena described for well-studied areas such as the Mississippi River (i.e. dip-feeding and autocyclicity) were uncritically extrapolated to other areas and assumed to be valid for all other members of the socalled delta category.

There are three major aspects that make sedimentation in the São Francisco strandplain very different from the classical deltas.

(i)
Sea-level history for the east coast of Brazil is characterized by a maximum around 5100 years ago when sea level reached 5 m above the present level. This sea-level history has exerted a major control on the evolution of the São Francisco Quaternary plain. During the 5.1 ka highstand the coastal plain was drowned and a barrier island/lagoonal system formed. When sea level dropped afterwards the shoreline prograded and Holocene beach ridges were deposited. As a result, sand body distribution is intimately controlled by sea-level history.

(ii)
In wave-dominated environments, the fluvial effluent behaves effectively as a groyne, retaining in the updrift side sediments transported shorewise by the longshore currents. This phenomenon creates a clear asymmetry in facies distribution at the Quaternary plain. Whereas the updrift side is characterized by a continuous sand sheet, progradation on the downdrift side occurs by incorporation of sandy islands (reworked river-mouth bar sediments) that extend coastwise, protecting small lagoons rapidly filled by suspended sediments. This manner of sediment dispersal is also reflected along the entire shoreline and inner shelf in the vicinity of the river mouth. Therefore, the São Francisco ‘delta’ is not simply a dip-fed system. In the updrift side progradation of the shoreline is accomplished with sediment contribution from outside sources.

(iii)
Autocyclic processes such as changes in the lower river course (the delta cycle concept) have not been observed for the São Francisco strandplain.
The influence of inherited geological framework upon a hardbottom-dominated shoreface on a high-energy shelf: Onslow Bay, North Carolina, USA
Authors: Cleary W. J. , Riggs S. R. , Marcy D. C. , Snyder S. W. 
Published: September 2007

Abstract
The southeastern coast of North Carolina is a major tourist destination that has experienced rapid population growth resulting in increased revenues. Most development is sited on transgressive barriers and headland beaches located along chronic erosion zones. Beach replenishment is viewed as the only viable option for erosion mitigation. However, a detailed sand resource assessment is non-existent. Furthermore, few data exist on the inter-relationships between the underlying geological framework and the morphology, sediments and evolution of the coastal system.
The shoreface of the two constraining headlands of this sand-starved system in Onslow Bay was studied utilizing cores, remotely sensed data, and diver surveys. The (coquina-dominated) subaerial headland at Fort Fisher and the (limestone) submarine headland at New River clearly have influenced the coastwise evolution of the intra-headland perched beaches. These shorefaces, as well as those of adjacent barriers, are characterized by hardbottoms of varying relief, morphology, and lithology. Prominent submarine scarps and karstic topographic highs that extend above the ravinement surface have resulted in major changes in barrier orientation and development of distinct subcompartments with respect to coastal processes.
Holocene sea-level rise has produced a thin (<70 cm) variable sequence, deposited unconformably over bioeroded hardbottoms. Bioerosion represents a major source and supply of new sediment. The thin sediment veneer is a mosaic of remobilized graded palimpsest and residual shell-rich sand and gravels. Data reinforce the concept that a common equilibrium profile for all shorefaces is neither realistic nor adequate for an understanding of coastal processes in the study area.
Radiometry as a technique for use in coastal research
Authors: De Meijer R. J. , Tánczos I. C. , Stapel C. 
Published: September 2007

Abstract
Natural radioactivity in certain heavy minerals makes it possible to locate and follow, in time and space, such components in coastal sands. In this paper, the sensitivity of radiometric techniques is demonstrated in measurements carried out in the laboratory and in the field. In the laboratory, on the beach and on the sea floor, indications were found that transport processes acting on light and heavy minerals often result in net transport modes in opposite directions. A simplified transport model is discussed which describes this selective transport semi-quantitatively. This model calculates trajectories of individual grains, using physical expressions for the forces acting on them. The model incorporates turbulence and vortex motion in an effective viscosity coefficient.
Genetic diversity of manganese deposition in the terrestrial geological record
Authors: Roy Supriya 
Published: September 2007

AbstractTerrestrial manganese deposits formed by hydrothermal, sedimentary and supergene processes. Ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction-related settings and those deposited from terrestrial hot springs are discussed. Sedimentary Mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea-level changes. Mn carbonate deposits probably formed by diagenesis through Mn oxyhydroxide reduction coupled with organic matter oxidation. Climatic variation, and basin water stratification, responsible for Mn concentration, were manifestations of atmospheric CO2content prompted by tectonism. Supergene manganese enrichment in continental weathering profiles was mainly dictated by climate, topography and drainage systems.
Fractionation of manganese from iron in Archaean and Proterozoic sedimentary ores
Authors: Glasby G.P. 
Published: September 2007

Abstract
The fractionation of manganese from iron through geological time has previously not been well understood. Iron deposits were considered to be abundant in the Precambrian and have declined in the Phanerozoic whereas manganese deposits appeared to show the opposite trend.
It is now seen that the Proterozoic banded iron formations contain about 200 times the amount of manganese in land-based manganese deposits and an order of magnitude more manganese than in deep-sea manganese nodules. The great abundance of manganese in these banded iron formation appears to resolve this problem.
In the Archaean and Proterozoic oceans, hydrothermal activity played a much more important role than at present due to the higher geothermal gradients. Upwelling of hydrothermally-derived iron, silica and manganese from anaerobic oceanic basins to more oxygenated shallow platform areas may have provided the unique conditions required for the formation of the Proterozoic banded iron formations which constitute the largest mineable reserve of any metal. An important factor in the formation of these deposits was the low sulphate ion content of the ocean waters. This ensured that the iron did not precipitate dominantly as pyrite under the reducing conditions then prevalent in the ocean waters. Manganese and iron could therefore display similar aqueous geochemistries. The reason for the separation of manganese from iron to form giant manganese deposits such as the Kalahari manganese deposit remains uncertain but variable redox conditions resulting from transgression and increasing atmospheric oxygen content or the influence of extensive hydrothermal activity may have been involved. Nonetheless, the similarity in the geochemistries of manganese and iron in the Palaeoproterozoic contrasts with the situation encountered in Phanerozoic manganese deposits in which iron became immobile in adjacent anoxic basins as pyrite thus ensuring the fractionation of manganese from iron. Oxidation of the ferrous ion could have taken place as a result of photosynthesis or of inorganic photochemical reactions. The formation of oxygen by these processes could have been the rate-determining step in the formation of the banded iron formations. It is possible that blooming by blue-green algae played a key role in the oxidation of the ferrous iron in the seawater. The seasonability of this blooming would then have resulted in the characteristic iron-rich and iron-poor microlaminae of these deposits.