bluuebunny/crossref_metadata_2025 huggingface dataset:
Deglaciation of the inner Scotian Shelf, Nova Scotia: correlation of terrestrial and marine glacial events
Authors: Stea R. R. , Boyd R. , Costello O. , Fader G. B. J. , Scott D. B.
Published: September 2007

The inner continental shelf off Nova Scotia is an important region for correlating glacial events across the terrestrial-marine transition. The inner Scotian Shelf can be subdivided into five coast-parallel terrain zones which record glaciation and the rise and fall of relative sea levels during the late glacial period. During the initial deglaciation phase (c.17–15 ka) ice was drawn out of the Gulf of Maine, isolating an ice mass over Nova Scotia which later became an active centre of outflow (Scotian Ice Divide). The Scotian Shelf End-Moraine Complex (SSEMC) formed at the margin of this glacier. Landward of the end moraine complex is a series of linear depositional basins termed the Basin Zone, containing a complete sedimentary record of events after deposition of the SSEMC. The lowest depositional sequences (sequences 1 and 2) in these basins are interpreted to be ice-proximal sediment, deposited by overflow and interflow meltwater plumes emanating from the retreating ice margin. From 13–12 ka, the sea level dropped rapidly due to glacial isostatic recovery. Ice receded out of marine areas, depositing the glacial-marine sequence 3 in the Basin Zone. A lowstand shoreline (c.11.6 ka) at −65 m is marked by the landward transition from morainal topography to a shoreface ramp, terrace and wave-cut platform. Enhanced current erosion during the lowstand was recorded in the inner Scotian Shelf basins by erosional truncation of sequence 3. After this erosional event the sea level rose rapidly, concomitant with climatic warming, as indicated by foraminifera within the Basin Zone and increases in spruce pollen in cores from Nova Scotia lakes. In the Basin Zone a seismic sequence characterized by indistinct, low-amplitude reflections (sequence 4) was deposited. Increased storminess and current sediment delivery with increased sea ice and icebergs during the Younger Dryas climatic cooling (c.11–10.0 ka) produced sequence 5 in the Basin Zone. Sequence 5 is correlative with a distinctive mineralic layer in lakes and periglacial and glacial sediments that overlie peat in land sections. The terrestrial and marine sections record a transition from organic-rich to inorganic sedimentation events initiatedc.10.8 ka. Climatic cooling and snowfield/glacier build-up on land, with increased meltwater runoff and storm-induced sedimentation in the marine realm, were the principal causes of these sedimentation events.
Deep-sea ostracode shell chemistry (Mg:Ca ratios) and Late Quaternary Arctic Ocean history
Authors: Cronin Thomas M. , Dwyer Gary S. , Baker Paul A. , Rodriguez-Lazaro Julio , Briggs William M.
Published: September 2007

The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus
Krithe
obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for palaeoceanographic study. Shells from the Polar Surface Water (−1 to −1.5°C) had Mg:Ca molar ratios of about 0.006–0.008; shells from Arctic Intermediate Water (+0.3 to +2.0°C) ranged from 0.09 to 0.013. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation (
r
2
= 0.59) between Mg:Ca ratios and bottom-water temperature in
Krithe
shells from Arctic and Nordic seas from water depths <900 m. Late Quaternary
Krithe
Mg:Ca ratios were analysed downcore using material from the Gakkel Ridge (water depths 3047 and 3899 m), the Lomonosov Ridge (water depth 1051 m) and the Amundsen Basin (water depth 4226 m) to test the core-top Mg:Ca temperature calibration. Cores from the Gakkel and Lomonosov ridges display a decrease in Mg:Ca ratios during the interval spanning the last glacial/deglacial transition and the Holocene, perhaps related to a decrease in bottom water temperatures or other changes in benthic environments.
North Atlantic sea surface conditions during the Younger Dryas cold event
Authors: Duplessy J. C. , Labeyrie L. D. , Paterne M.
Published: September 2007

A map has been drawn of the oxygen isotopic composition (
δ
18
O) of planktonic foraminifera which deposited their shells in isotopic equilibrium with ambient surface waters during the Younger Dryas cold event. These
δ
18
O values were derived from the
δ
18
O values of
Neogloboquadrina pachyderma
(left coiling) and
Globigerina bulloides
, which lived in their respective optimum temperature ranges. This map reflects the main trends of the sea surface temperature field during the Younger Dryas, but does not exhibit any
δ
18
O anomaly associated with continental ice-sheet melting. This result rules out all the theories relating the Younger Dryas cooling to injection of continental ice-sheet meltwater with very low
δ
18
O value into the North Atlantic Ocean. This reconstruction suggests that drifting of Arctic sea ice transported by the East Greenland Current may be a possible cause for the strong cooling which occurred in the middle of the last deglaciation.
Late glacial-Holocene sea surface temperatures and gradients between the North Atlantic and the Norwegian Sea: implications for the Nordic heat pump
Authors: Koç Nalân , Jansen Eystein , Hald Morten , Labeyrie Laurent
Published: September 2007

A S-N transect of sediment cores is used to (a) determine the millenial scale variability of sea surface temperatures (SSTs) and (b) the strength of the S-N SST gradients in the North Atlantic. The results show that the initial warming of the surface North Atlantic after the Last Glacial Maximum occurred synchronously between 50°N and 63°N at 13.4ka, but was delayed by 1000 years at 72°N. All cores indicate that the Bølling-Allerød period was a climatically unstable time interval punctuated by several SST coolings. However, the magnitudes of these brief coolings were strongly subdued in the North Atlantic compared with the eastern Norwegian Sea. Plotting SSTs on a S-N transect indicates the presence of a strong (9°C) gradient (the Arctic front) between the Norwegian Sea and the North Atlantic throughout the Bølling-Allerød period. This gradient became even stronger (15°C) during the Younger Dryas, and nearly disappeared during the Early Holocene. The observed SST gradients have implications for the magnitude of the oceanic heat pump and atmospheric circulation patterns of the late glacial period.
Late glacial sedimentology, foraminifera and stable isotope stratigraphy of the Hebridean Continental Shelf, northwest Scotland
Authors: Austin W. E. N. , Kroon D.
Published: September 2007

The detailed stratigraphies of two shallow marine cores from the Hebridean shelf of northwest Scotland are presented. The results provide evidence on the timing of deglaciation from about 15.2 ka
BP
, with evidence of cold, low salinity water persisting on the shelf until at least 13.5 ka
BP
. After 13.5 ka
BP
, probably shortly before 13.0 ka
BP
, warm shallow shelf seas were established and persisted throughout much of the interstadial. There is some evidence for climatic instability during the interstadial and for a cooling trend from after 11.6 ka
BP
. Glacial isostatic rebound of the shelf seems to have kept pace with eustatic sea level rise until about 11 ka
BP
.

The fully developed conditions of the Younger Dryas stadial are not observed until 11 ka
BP
. For the first time from the marine record the constituent tephra peaks of North Atlantic Ash Zone 1 are resolved into a sequence of eruptive events and demonstrate that extensive sea ice transgressed the western UK continental shelf throughout the Younger Dryas. The climatic conditions of the Younger Dryas persist until an initial, precursor warming at 10.2 ka
BP
, followed by a marked warming of about 8°C and fully established early Holocene temperatures before 10 ka
BP
. Many of the changes recorded through nearly 5 m of sediments accumulated during the Younger Dryas can be related to changing relative sea levels and source supply.
Marine mollescan proxy data applied to Scottish late glacial and Flandrian sites: strengths and limitations
Authors: Peacock J. D.
Published: September 2007

Knowledge of modern benthonic marine molluscs found in shallow water enables their distribution to be correlated with hydrographic conditions and the derived proxy data applied to late Quaternary assemblages. The application of such data for bottom temperature, minimum sea surface temperature and minimum salinity to four Flandrian and Late glacial sites shows that it is possible to follow changes in these parameters with time, in some cases in considerable detail. The chief limitations are that faunas from some boreholes and sections are sparse and of low diversity and that few taxa are restricted to narrow ranges of temperature and/or salinity. Where fossils of stenothermal and stenohaline species are absent from a profile, faunal analysis inevitably yields a less than precise picture of conditions. It is possible to give only generalized constraints on water depth because this is not a prime factor controlling the distribution of molluscs on the seafloor today. The palaeoenvironmental analysis of the four sites is briefly discussed in a wider context.
Late glacial sea level and ocean margin environmental changes interpreted from biostratigraphic and lithostratigraphic studies of isolation basins in northwest Scotland
Authors: Shennan Ian , Rutherford Mairéad M. , Innes James B. , Walker Kevin J.
Published: September 2007

Detailed biostratigraphic and lithostratigraphic analyses from isolation basins at Ardtoe, Rumach, Loch nan Eala and Fearnbeg, northwest Scotland, allow an interpretation of sea level movements and environmental changes within the Lateglacial Interstadial and Younger Dryas (13-10 ka
BP
). Microfossil analyses illustrate the gradual transition of the isolation basins from marine basins to freshwater lakes within an area of isostatic uplift. These data provide evidence for a fall in relative sea level in northwest Scotland from the mid-Lateglacial Interstadial to the early Holocene.

Pollen, diatom and dinoflagellate cyst (dinocyst) analyses link the oceanic record of major climate and oceanic circulation changes with the terrestrial biostratigraphic record. Movement of the oceanic Polar Front west and north during a period of relative climatic amelioration within the Lateglacial Interstadial and a corresponding change in the position of the North Atlantic Current may be inferred from the dinocyst record. This is followed by a relative cooling.
Late Weichselian environmental changes of the southern Kattegat, Scandinavia, inferred from diatom records
Authors: Jiang Hui , Nordberg Kjell
Published: September 2007

The diatom stratigraphy of a high-resolution sediment core, dated by the tandem accelerator mass spectrometry (AMS)
14
C method, records the environmental changes of the Late Weichselian in the southern Kattegat. Five diatom assemblage zones, with two subzones, are distinguished during the Allerød and Younger Dryas chronozones. Fresh water diatoms dominate the assemblages throughout the core. Salinities, particular the surface water salinity during the whole period, were much lower than that of today. Between 11 500 and 11 300 years bp, the occurrence of abundant freshwater planktonic species with only a few brackish water and marine species suggests an environment strongly affected by a great amount of meltwater discharged from the Baltic Ice Lake via the Öresund Strait. The period from the late Allerød to the early Younger Dryas between 11 300 and 10 600 years bp is characterized by an incursion of cold, saline water into the southern Kattegat with the strongest phase between 11 300 and 10 900 years bp, mirrored by increasing marine diatoms, especially sea ice species. Climatic amelioration took place at about 10 650 years bp, which occurred synchronously with a hydrographic change in the southern Kattegat. Relatively warm marine water, mixed with cold marine water, flowed into the Kattegat, although its impact on the southern Kattegat was small. Towards the end of this stage, the influence of saline water on the southern Kattegat became weaker, and a large amount of meltwater was discharged from the Baltic Ice Lake, which resulted in the surface water salinity decreasing greatly. An earlier change in the drainage pathway of the Baltic Ice Lake, from the Öresund Strait to south central Sweden, took place between 11 200 and 10 900 years bp. This was suggested by fewer planktonic freshwater diatoms and low sediment accumulation rates and/or a hiatus.
Palaeoceanography on the European arctic margin during the last deglaciation
Authors: Hald Morten , Dokken Trond , Hagen Sveinung
Published: September 2007

To reveal the palaeoceanographic and palaeoclimatic evolution related to the disintegration of the Barents Sea and Fennoscandian ice sheets, high-resolution sediment cores from the continental margin off western Svalbard, western Barents Sea and northern Norway were investigated. The location of these cores is below the axis of the Norwegian Current and beyond, but close to, glaciated continental areas. Hence they should sensitively reflect the palaeoceanography of the northernmost Norwegian Sea. Between, 14.5–19.5 and 22.5–29
14
C ka, a high abundance of planktonic foraminifera and a small content of subpolar species indicate seasonally ice-free and slightly warmed surface water. This phenomenon is related to the advection of surface water of North Atlantic origin. The onset of the deglaciation is characterized by a marked low oxygen event dated to between 15 and 13 ka, interpreted to reflect a surface water freshening produced by meltwater and reduced oceanic mixing. After the onset of deglaciation, the surface ocean warmed in three rapid steps: (1) around 12.5 ka, indicated by increased abundances of planktonic foraminifera; (2) at 10.2 ka and at (3) 10–9.6 ka. The two latter steps are reflected by the increased abundance of subpolar planktonic foraminifera.
Post-glacial environments of the southeastern Barents Sea: foraminiferal evidence
Authors: Polyak Leonid , Mikhailov Valery
Published: September 2007

Quaternary sediment records from the southeastern Barents Sea were used to reconstruct palaeoceanographic environments since the last deglaciation based on lithology, foraminiferal assemblages and AMS
14
C dates. After the ice sheet retreat at 13 ka
BP
two pulses of glacimarine sedimentation occurred, separated by non-deposition between approximately 12 and 10.5 ka
BP
. Proximal sedimentation from meltwater overflows prevailed during the first pulse, whereas the second pulse reflects distal glacimarine environments with some inflow of Atlantic water. Full marine environments were established by 9.3 ka
BP
, associated with increased Atlantic water advection, intensified currents and reduced sedimentation rates. The maximum Atlantic influence lasted until approximately 5 ka
BP
, followed by an advance of Arctic surface water with winter sea ice cover.
Palynology as a tool for land-sea correlation; an example from the eastern Mediterranean region
Authors: Zonneveld Karin A. F. , Boessenkool Karin P.
Published: September 2007

Sediments from two cores from the Adriatic Sea (Eastern Mediterranean), deposited between 18 and 9 ka
BP
, have been investigated with respect to their marine (dinoflagellate cyst) and terrestrial (pollen) fossil content. Based on contemporaneous changes in both the dinoflagellate cysts and pollen associations, a paleoclimatic reconstruction of the Adriatic Sea region is constructed for the studied time interval. Several intervals with increased Po River discharge are identified which may be subscribed to melting phases of the glaciers in the Alps and Apennines or increased winter precipitation in the region.
Earth rotation, ocean circulation and palaeoclimate: the North Atlantic — European example
Authors: Mörner Nils-Axel
Published: September 2007

The glacial eustatic rise in sea level after the 20 ka
BP
glaciation maximum led to an increase in the equatorial radius and hence a general deceleration in the Earth’s rate of rotation. The sea-level rise can be approximated by two superposed exponential curves with a transitional period about 13-10 ka radiocarbon years
BP
. This period is known to cause high-amplitude climatic changes and regionally irregular changes in sea level. This is interpreted as a break down in the Earth-Moon adjustment to the post-glacial deceleration, which was instead compensated by rapid re-distributions of oceanic water masses and interchanges of angular momentum between the hydrosphere and the solid Earth. At about 6000 years
BP
the glacial eustatic rise in sea level ended and a new set of circumstances began, which were characterized by feedback interchanges of angular momentum between the solid Earth and the hydrosphere. It is proposed that the palaeoclimatic changes on a decadal to millennial time-scale are primarily driven by the causal connection between the Earth’s rotation, oceanic circulation, ocean/atmosphere heating, atmospheric (wind) heat transport and continental palaeoclimatic changes.
Sequence and systems tract interpretation of the epicontinental Oligocene deposits in the Danish North Sea
Authors: Michelsen O. , Danielsen M.
Published: September 2007

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

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

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

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

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

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

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

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

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

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

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

Terrestrial 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

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.
Mineralogy and geochemistry of Archaean greenstone belt-hosted Mn formations and deposits of the Dharwar Craton: Redox potential of proto-oceans
Authors: Manikyamba C. , Naqvi S.M.
Published: September 2007

Late Archaean greenstone belts of the Dharwar supergroup are uniquely characterized by a marker horizon that consists of Fe + Mn formations, carbonates (± stromatolites), and phyllites (± organic matter). Microfossils are found in cherts associated with stromatolites and banded Fe-Mn carbonate. Manganese-bearing arenites-argillites-carbonates have a varied mineralogy that is reflected by variations in chemical composition. Trace elements characteristic of felsic and volcanic rocks such as Zr, Hf, Rb, Sr, U, Th, Ni, Cr, Co, V, and Sc are low or high depending on the amount and type of clastic debris deposited with the chemical precipitates. REE also are influenced by the clastic fluvial and hydrothermal fluxes. Banded Fe + Mn carbonate-chert rocks (BMF) contain lower amounts of REE compared to samples containing ripidolite, which have higher Al2O3, ΣREE, Zr and Hf contents. Both positive and negative Eu, La and Ce anomalies are observed which reflect variable mixing of hydrothermal solutions with ambient ocean water and divergent clastic material. The data indicate that FeO, MnO and SiO2were added to the Archaean proto-ocean by hydrothermal solutes produced along a spreading ridge axis. The redox potential of these proto-oceans was very low near the ridge axis, but increased towards the shelf, due to higher organic productivity and photosynthesis reflected by the presence of stromatolites, organic matter, and microbiota. Precipitation of stable Mn oxides at the margin of the greenstone belts is probably the consequence of the high redox potential.
Manganese ores of the Ghoriajhor-Monmunda area, Sundergarh District, Orissa, India: geochemical evidence for a mixed Mn source
Authors: Nicholson Keith , Nayak V. K. , Nanda J. K.
Published: September 2007

The Proterozoic sedimentary manganese ores of the Gangpur Series, Orissa, India are of gonditic type and are variable in size, depth and grade of ore. The host sediments were deposited in a shallow shelf environment, as reflected in the variable clastic input into the sequence. Braunite and hollandite are the principal ore minerals, with bixbyite, rare jacobsite and rare vredenburgite. Manganese minerals in the gondites are spessartine and rhodite, together with quartz and aluminosilicates. Supergene weathering and enrichment of the ore horizon and gondite produced secondary ores composed of cryptomelane and pyrolusite. The geochemistry of the deposits shows Mn/Fe≈4, low trace element concentrations and arsenic enrichments that exceed 3000 mg kg
−1
. These are interpreted as indicating a mixed hydrogenetic-hydrothermal source for the manganese oxides of the original precurser (pre-metamorphism) sediments. Regional metamorphism to amphibolite grade transformed this variable oxide-clastic sequence into manganese ores, sharply interbedded with gondites.
Iron and manganese oxide mineralization in the Pacific
Authors: Hein James R. , Koschinsky Andrea , Halbach Peter , Manheim Frank T. , Bau Michael , Kang Jung-Keuk , Lubick Naomi
Published: September 2007

Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ΣREEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ΣREE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.
Some controls on the geochemical variability of manganese nodules with particular reference to the tropical South Pacific
Authors: Cronan D. S.
Published: September 2007

Superimposed on traditional controls on manganese nodule compositional variability, such as metal source and nodule mineralogy, are additional controls related to biological productivity, water depth, the depth of the calcite compensation depth (CCD) and the nature of the associated sediments. Fluxes of Mn, Ni, and Cu to the nodules increase in equatorial regions of high biological productivity but high values of these metals in south equatorial Pacific nodules appear to occur only within about 200 m of the CCD. This is thought to result from the concentration of labile organic matter there, the decay of which fuels the diagenetic reactions leading to Mn, Ni, and Cu enrichment in the nodules. However, this process appears to be at its most intense on the flanks of the South Pacific equatorial high productivity zone. Under the most highly productive waters, Mn, Ni, and Cu rich nodules do not occur at any depth nor are nodules abundant there. This is thought to be due to the presence of biogenic silica, the concentration of which is not depth dependent, as the main diluent of the labile organic material at depths near and below the CCD under the most highly productive waters.