Distal Glaciomarine Research Articles

Late Cryogenian and late Paleozoic ice ages on the São Francisco craton, east Brazil

The miniature paleocontinent in the region of the São Francisco River valley, in eastern Brazil, holds the record of two different glacial epochs. The late Cryogenian Jequitaí Formation from the Bambuí Group is up to 100 m thick and covers areas mainly in the central São Francisco craton. Evidences for glacial sedimentation are beautifully preserved E-W grooves and striations, dropstones within fine-grained rocks, and a full set of diamictites enclosing a rich and complex depositional history. The Jequitaí Formation is in close link with the tectonic evolution of the São Francisco paleocontinent and the West Gondwana amalgamation. From west, the precocious Paranapanema and São Francisco blocks collision in late Cryogenian flexured the foreland lithosphere and created depozones that were infilled by glacial sediments. Toward east, the rifting and opening of the Adamastor Ocean allowed thick glacial and non-glacial deposits to form through subaqueous gravitational sedimentation. From west to east, proximal and distal glaciomarine, glaciocontinental, and non-glacial resedimentation are identified and linked to the evolving continental masses and climate during the Cryogenian and beginning of Ediacaran. The late Paleozoic Santa Fé Group is the youngest record of glaciation on the São Francisco craton. It is 60–80 m thick and yields consistent and confident glacial evidences such as N-S striations on top of Cambrian sandstones, ice-rafted debris, and rain-out diamictite, all preserved in small and patchy areas in the west-central São Francisco craton. Paleocurrents suggest a northern ice center and sedimentary facies indicate deposition in continental lakes and rivers. Although late Paleozoic, its age is poorly constrained and likely correlated with the uppermost Itararé Group (Taciba Formation) of Paraná Basin in south Brazil. Deglaciation and strong isostatic adjustments make up the termination of the Santa Fé Group sedimentary record and depict a glaciocontinental system evolved on an interior stable continental crust. The late Neoproterozoic Jequitaí Formation and the late Paleozoic Santa Fé Group are parts of the earth’s sedimentary history preserving a rich record of climate, tectonic, and surface processes in part controlled by the evolving continental masses on the São Francisco craton.

Sequence stratigraphy of the Cryogenian Nantuo Formation in South China: Constraints on Marinoan glaciation dynamics

• Diverse sedimentary environments capture the evolution of Marinoan glaciation . • These Marinoan deposits record two complete, symmetrical sedimentary cycles. • Patterns of cyclic environmental changes are consistent with global-scale controls. • Marinoan glaciation gradually transited into the Ediacaran greenhouse. Cryogenian low-latitude glaciations mark the ‘Snowball Earth’ events and were thought to be dynamic on the basis of sedimentary features, especially glacial cycles. Although the glaciation dynamics and associated environmental changes can be investigated through the sedimentary records, there are sparse sedimentary studies. Studies from the Marinoan deposits in South China provide the basis for establishing a sequence stratigraphic framework that includes two complete glacial cycles across a basin-to-platform transect. Both cycles are characterized by symmetrical facies patterns, with a lower ice-advance succession and an upper ice-retreat succession. Each ice-advance succession consists primarily of a massive diamictite lithofacies association, and is dominated by proximal glaciomarine deposits. The gravel abundance and size of the deposits increase upward gradually, suggesting a progradational sequence. Each ice-retreat succession is composed of both a massive diamictite lithofacies association and a fine-grained lithofacies association, representing a mix of distal glaciomarine, proximal glaciomarine, and non-glacial marine deposits. The gravel abundance and size of these varied deposits decrease upward gradually, interpreted to reflect a retrogradational sequence. This sequence stratigraphic framework, interpreted to reflect gradual alternation from ice advance to ice retreat, indicates dynamic co-evolution of the sedimentary environments, paleoclimate, and sea level during the Marinoan glaciation. The glaciation dynamics, as they are reflected globally, highlight a gradual transition from the Marinoan glaciation to the Ediacaran greenhouse, and indicate a time lag between the onset of the deglaciation and the formation of the cap carbonates.

Constraints on the nature of the Marinoan glaciation: Cyclic sedimentary records from the Nantuo Formation, South China

Detailed sedimentological investigations of the Cryogenian glacial deposits are critical for constraining the true nature of the Sturtian and Marinoan glaciations. The entire succession of the Nantuo Formation, which corresponds to the Marinoan glaciation, is well developed in South China. Here a detailed lithological and sedimentological analysis of two cores of the Nantuo Formation in Guizhou, South China, is presented in which two continuous ice advance–retreat cycles are identified. The base consists of a massive diamictite lithofacies that is representative of glacier-dominated subaqueous debris flow deposits. These proximal glaciomarine deposits are overlain by a gravel-free sandy mudstone lithofacies that is lacking in diamictites, which implies distal glaciomarine deposits. This ice advance–retreat sedimentary cycle is overlain by a weakly laminated diamictite lithofacies, which represents subaqueous debris flow deposits that formed during the second episode of ice advance. These proximal glaciomarine deposits are overlain by an interbedded sandstone–mudstone lithofacies, which is indicative of distal glaciomarine deposits that formed during another episode of ice retreat. These sedimentary cycles imply that the climate switched twice from relatively warm to extremely cold and back during the Marinoan glaciation. The global sea-level and sedimentary environments fluctuated in response to these climate changes. This co-evolution of the climate, sea-level, and sedimentary environments, which is represented by the lithofacies and sedimentary sequence of the Nantuo Formation, as well as the corresponding strata of other sections worldwide, suggests that the Marinoan glaciation is characterized by a progressive and dynamic course.

Retreat of the Smith Sound Ice Stream in the Early Holocene

Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.

Cyclic cold climate during the Nantuo Glaciation: Evidence from the Cryogenian Nantuo Formation in the Yangtze Block, South China

Geological and paleomagnetic data indicate that the ice sheets might have extended to low-latitude regions in the Cryogenian (720–635 Ma). The ‘snowball Earth’ hypothesis proposed that the Earth was completely ice-covered during global glaciation. However, the glacial sedimentary record seems to contradict with the snowball Earth hypothesis. Detailed sedimentological investigations of the glacial deposits would provide the first-order constraint on the nature of global glaciation. The Nantuo Formation (∼654–635 Ma) in the Yangtze Block of South China has been correlated with the Marinoan snowball Earth. In this study, we conducted systematic sedimentological analyses of six sections/cores of the Nantuo Formation. Three facies associations were recognized: the proximal glaciomarine, distal glaciomarine, and non-glacial marine facies associations. The vertical stacking pattern of facies associations can be correlated among the five slope and basin sections, while their correlation with the shelf section remains obscure. Our data indicate two episodes of glaciation that are separated by an interglacial interval during the Nantuo Glaciation. The first glacial episode is recorded by successions of coarse-grained facies (e.g., massive diamictite) in the lower part of the Nantuo Formation. The re-appearance of massive diamictite in the middle to upper part of the Nantuo Formation indicates onset of the second glacial episode. These two glacial episodes were separated by a siltstone/shale sequence of several 10 s m thick, suggesting an interglacial period with limited influence from glaciation. The top of Nantuo Formation consists of alternative distal-glaciomarine and non-glacial marine facies associations, representing the deglacial sequence of the Nantuo Glaciation. The sedimentary facies analysis indicates that the cold climate during the Nantuo Glaciation may be cyclic. Finally, our sedimentary analysis confirms a lag between the deglaciation and precipitation of cap carbonate.

Slow net sediment accumulation sets snowball Earth apart from all younger glacial episodes

Abstract During the Sturtian and Marinoan “snowball Earth” episodes, ice cover is thought to have extended from polar to tropical latitudes. We test the supposition that such an extreme glacial climate, not repeated in the subsequent ∼635 m.y. of Earth history, would have reduced the vigor of the hydrologic cycle and thus diminished sediment flux to the oceans. With >500 sediment accumulation rates to characterize Sturtian and Marinoan deposits, we find median accumulation rates at least four to 15 times slower than expected for Phanerozoic glaciomarine deposits as characterized by >10,000 rates. Our comparison is conservative with respect to time span, latitude, and distance from the ice margin. Phanerozoic accumulation rates decrease systematically when averaged over longer time spans. Comparisons were drawn, therefore, at 5 and 57 m.y. time spans to match minimum Marinoan and Sturtian durations, respectively. Cenozoic glaciomarine accumulation also slows with increasing latitude from temperate to polar climates and with increasing distance from the ice margin. After accounting for time span, snowball Earth deposits at low latitude are found to be thinner than would be expected either for high-latitude Cenozoic glacial deposits or for very distal glaciomarine abyssal muds with ice-rafted debris. The rate discrepancy is not readily attributed to overestimates of the total Marinoan or Sturtian durations. If sediment fluxes during warm melt intervals did approach Phanerozoic rates, these intervals must have occupied a much smaller proportion of snowball Earth episodes than in younger glacial climates.

Lateglacial ice extent and deglaciation of Loch Hourn, western Scotland

Synopsis Loch Hourn is a 21 km-long fjord on the west coast of Scotland. A multibeam survey of the outer Loch Hourn basin extending into the adjacent Sound of Sleat reveals a series of moraines beyond the fjord mouth relating to the Scottish ice cap during the Lateglacial period ( c . 15–11 cal ka BP). The outermost moraine is located in the Sound of Sleat, 3.5 km beyond the currently accepted limit of Younger Dryas Stadial glaciation in the loch. Sediment cores from the main outer basin of the fjord sample four lithological units: a coarse-grained basal sand, interpreted as an ice-proximal deposit; finely laminated silts containing occasional clasts, interpreted as a distal glaciomarine unit deposited through pelagic settling from glacial meltwater and turbidity current activity; a poorly sorted mixture of muddy sands containing convolute bedding and flame structures, interpreted as slumped glacigenic material; and poorly sorted, bioturbated marine muds with mollusc shells ( Arctica islandica ) which yielded a basal radiocarbon date of 11.2 cal ka BP, indicating that open-marine conditions typical of the Holocene were established in the fjord by this time.

Chapter 49 The Neoproterozoic Macaúbas Group, Araçuaí orogen, SE Brazil

Abstract The Neoproterozoic Macaúbas Group records accumulation in the precursor basin of the Araçuaí orogen, located on the eastern margin of the São Francisco craton (SE Brazil). The Macaúbas basin evolved from a late Tonian continental rift to a passive margin that lasted at least until c. 660 Ma. It was orogenically inverted during the late Neoproterozoic Brasiliano event. The Macaúbas Group includes the pre-glacial Matão, Duas Barras and Rio Peixe Bravo formations, the glaciogenic Serra do Catuni, Nova Aurora and Lower Chapada Acauã formations, and the post-glacial Upper Chapada Acauã and Ribeirão da Folha formations. In the central sector of the Araçuaí orogen, the oldest glaciogenic unit of the group, the Serra do Catuni Formation, overlies the sandstone-conglomerate package of the Duas Barras Formation. The Serra do Catuni Formation consists of massive diamictite with minor sandstone and rare pelite, deposited mostly in a proximal glaciomarine environment. This unit passes upward and eastward into the Lower Chapada Acauã Formation, a thick succession of stratified diamictite, graded sandstone, pelite, transitional basalt and rare carbonate. This distal glaciomarine unit is covered by the diamictite-free Upper Chapada Acauã Formation, which passes eastward into the Ribeirão da Folha Formation, which includes fine-grained turbidite, pelite and ocean-floor rocks. In the northern sector of the Araçuaí orogen, the sandstone-pelite succession of the pre-glacial Rio Peixe Bravo Formation is covered by the Nova Aurora Formation, the glaciomarine unit rich in diamictite and Fe-rich diamictite, with minor graded sandstone and rare pelite. The Nova Aurora Formation is covered by the sandstone-pelite package of the Upper Chapada Acauã Formation. The pre-glacial and glaciogenic successions record the continental rift to transitional stages of the Macaúbas basin. The post-glacial succession represents proximal and distal passive margin to ocean floor environments. The Serra do Catuni Formation seems to be a proximal glaciomarine equivalent of the Jequitaí glacio-terrestrial deposits located on the São Francisco craton.

Glacial events in Carboniferous sequences from Paganzo and Río Blanco Basins (Northwest Argentina): Palynology and depositional setting

The age and depositional setting of two glacial events recognized in the western basins of Argentina are discussed in this paper. The older one corresponds to diamictites identified in the upper member of the Cortaderas Formation (Visean, Rio Blanco Basin). The glacial sequence consists of shales, dropstone-bearing shales massive matrixrich diamictites, massive clast-rich diamictites, and stratified diamictites, all of them interpreted as deposited in distal glaciomarine settings. Palynological remains recovered from shales interstratified with diamictites were referred to the late Visean Reticulatisporites magnidictyus-Verrucosisporites quasigobbettii Biozone. Younger glacial deposits were studied at the base of the Guandacol Formation (Paganzo Basin) where are made up by clast-poor massive diamictites, clast-rich massive diamictites, stratified diamictites, thinly-bedded dropstonebearing diamictites, rhythmites, dropstone-bearing shales, and barren of dropstone shales. The whole sequence is interpreted as deposited in low-relief proximal glaciomarine environments (morainal banks). The abundant palynological assemblages found in the glacial interval were included in the subzone A of the Raistrickia densa- Convolutispora muriornata Biozone which is considered Serpukhovian-early Bashkirian in age. Palynological remains found in the Cortaderas Formation suggest that the beginning of the Glacial 2 event in Gondwana (according to Isbell’s chronological proposal for glacial and interglacial stages) should be considered late Visean while the end, according to the assemblages recovered from the Guandacol Formation, was not younger than early Bashkirian. Moreover, sedimentological and stratigraphic data suggest the existence of a short interglacial period between the Cortaderas and Guandacol glacial events.

Late Quaternary Paleoceanography and Sedimentary Environments in Hudson Strait

Airgun and high resolution Huntec seismic reflection profiles are interpreted to show up to 130 m of glacial, glaciomarine and postglacial sediments overlying bedrock. In a basin at the eastern entrance to Hudson Strait most of the surficial sediment was deposited during the last déglaciation, but in western Hudson Strait multiple till sequences from previous glaciations are recognized. Five acoustic units were identified, at least three of which were penetrated with piston cores. Foraminifera of the stratigraphically deepest core in the eastern basin indicate a proximal glaciomarine environment and a likely presence of an ice shelf. A 14C date of 8060 ± 70 yBP (TO 750) on molluscan shells gives a minimum age for the top of the acoustically laminated distal glaciomarine sediments. The early postglacial foraminifera suggest a period of increased influence of offshore bottom waters restricted to the deep eastern basin. The surface sediments of all cores contain species indigenous of colder and fresher inshore waters of the present time. The ratio of 18CV16O in the benthic foraminifer Cibicides lobatulus is herein related to bottom salinity. Downcore measurements of 8'8O on C. lobatulus tests indicate bottom paleosalinities lower by about 0.5%o shortly before the dated horizon of 8000 yBP. By this time Hudson Strait was sufficiently clear of glacial ice for establishment of the present tidal regime. The lower bottom salinities indicate that tidal mixing took place between glacial meltwater leaving Hudson Bay and the offshore counterflow. This process is thought to have reduced the sharpness of the salinity difference between the offshore water and the surface plume of Laurentide meltwater as it entered the ocean.

Relative Sea-Level Change in the Northern Strait of Georgia, British Columbia*

Twenty-four new radiocarbon dates from isolation basin cores, excavations and natural exposures, and an archeological site, constrain relative sea-level change since the last glaciation in the northern Strait of Georgia, British Columbia. Relative sea level fell rapidly from about 150 m elevation to 45 m elevation from 11 750 to 11 000 BP (13 750 to 13 000 cal BP), then its rate of fall slowed. The initial rapid emergence began soon after the transition from proximal to distal glaciomarine sedimentation, when the glacial front retreated from the Strait of Georgia and the Earth’s surface was unloaded. A sea-level lowstand a few metres below present-day sea level may have occurred in the early Holocene, but sea level was near its present level by 2000 BP. Sea-level change in the northern Strait of Georgia lagged the mid Strait of Georgia, 80 km to the south, by a few hundred years during initial emergence. The lowstand in the northern strait was later and probably shallower than in the mid strait. Isostatic depression inferred from the sea-level observations can be fit with two decaying exponential terms with characteristic decay times of 500 and 2600 years. The faster decay time corresponds to a shallow mantle viscosity of about 1019 Pa s, consistent with previous glacio-isostatic modelling. The present-day crustal uplift rate from the residual isostatic effects of the Cordilleran Ice Sheet is about 0.25 mm/a. Crustal uplift is not expected to significantly ameliorate projected sea-level rise in the mid and northern Strait of Georgia because present-day vertical crustal movements are inferred to be small.

Facies system of the Eastern Barents Sea since the last glaciation to present

Twenty-two sediment cores raised from the central and eastern parts of the Barents Sea have been studied to reconstruct the evolution of the facies system since the Late Weichselian glaciation. Multiproxy records reveal four lithostratigraphic units, which reflect major development stages of paleoenvironments. Age control is provided by 23 AMS 14C dates for Holocene sections of four cores. Continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase. During this phase, the Barents Sea ice sheet detached from the ground resulting in seawater penetration into troughs, iceberg calving, deposition of IRD and fine-grained glacier meltwater load in newly formed marine basins. The main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor IRD. Redistribution of fine-grained suspended matter by bottom currents and brine-induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the Holocene marine sediments. The Holocene facies of shelf depressions reflect rather high, but variable productivity responding to climate changes and variations of Atlantic water inflow into the Barents Sea.

Glaciomarine sedimentation and its paleoclimatic implications on the Antarctic Peninsula shelf over the last 15 000 years

Analyses of sedimentological, geochemical and micropaleontological parameters from radiocarbon-dated sediment cores retrieved from the Antarctic Peninsula’s western continental shelf reveal a detailed paleoclimatic and/or paleoceanographic history over the last 15 000 radiocarbon years. Deglaciation of the outer shelf off Anvers Island commenced prior to at least 15 000 yr BP, marked by the deposition of distal glaciomarine diamicton (facies 2) beneath a floating ice shelf, and lasted for 3800 years with increasing diatom abundance and total organic carbon (TOC) over time. A return to colder conditions occurred between 12 800 and 11 600 yr BP with a drop in TOC content and diatom abundance, which is coincident with the Younger Dryas event in the North Atlantic region. At this time, an abrupt increase in percentage sea-ice taxa as well as in the ratio of ( Fragilariopsis curta+Fragilariopsis cylindrus)/ Thalassiosira antarctica suggests renewed ice-shelf advance. In contrast, the inner shelf was deglaciated somewhat later about 11 000 yr BP, that is, 3000 years after the outer shelf. Prior to 11 000 yr BP, deposition of proximal glaciomarine diamicton (facies 1) close to the grounding line under a floating ice shelf and/or persistent sea ice may have occurred on the inner shelf. After this date, deposition of distal glaciomarine diamicton (facies 2) followed. A climatic optimum is recognized between 6000 and 2500 yr BP, coinciding with a ‘mid-Holocene climatic optimum’ from several other Antarctic sites, e.g. the Palmer Deep. During this time, as the glacial system receded from the shelf, greatly enhanced primary productivity occurred in open marine conditions, resulting in the deposition of diatomaceous mud (facies 3) and causing post-depositional dissolution of calcareous benthic and planktonic foraminifers in sediment. Around 2500 yr BP (the onset of the Neoglacial), diatomaceous sandy mud (facies 4), characterized by a decrease in TOC and diatom abundance, reflects the formation of more extensive and seasonally persistent sea ice, as evidenced by an increase in percentage of sea-ice taxa and in the ratio of ( F. curta+F. cylindrus) /T. antarctica. Our results provide evidence of climatic change on the Antarctic Peninsula’s western shelf that helps to refine the existence and timing of late Pleistocene and Holocene millennial-scale climatic events in the Southern Hemisphere.

Late Weichselian to Holocene paleoenvironments in the Barents Sea

Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north–south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 14C ka BP in the southern and about 9.2 14C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.

Neoproterozoic snowball Earth under scrutiny: Evidence from the Fiq glaciation of Oman

The Fiq Member of the Ghadir Manqil Formation, Huqf Supergroup, Oman, is composed of ∼1.5 km of glacial rainout diamictites, mass-flow deposits, turbiditic sandstones, and slope and shelf sandstones and siltstones, overlain by a classic <10-m-thick transgressive cap dolostone. Paleocurrents, facies distribution, and subsurface imagery show that the Fiq Member was deposited in a series of extensional half-grabens and grabens. Facies associations represent proximal glaciomarine, distal glaciomarine, nonglacial sediment gravity flow, and nonglacial shallow-marine siliciclastic depositional environments and processes. The member is divided into seven units that can be correlated across the rift basin. Although the facies mosaic is complex, cycles of relative sea-level change, most likely driven by glacio-eustasy, show that glacial advance and retreat during the glacial epoch was strongly pulsed. Only the final (youngest) diamictite is overlain by a well-developed cap carbonate. It is unlikely that there was any prolonged and substantial shutdown of the hydrologic cycle during deposition of the Fiq Member. On the basis of sedimentological and stratigraphic data, the Neoproterozoic glacials of Arabia were more like the familiar oscillatory glaciations of the Pleistocene than those required by the snowball Earth hypothesis.

Late Quaternary glacigenic contourite, debris flow and turbidite process interaction in the Faroe-Shetland Channel, NW European continental margin

Abstract The Faroe-Shetland Channel is an important conduit or gateway for the southward flow of cold bottom waters formed in the Norwegian Sea. This Norwegian Sea Overflow Water (NSOW) finds several spillover channels across the Wyville-Thomson Ridge, eventually descending into the northern Rockall Trough and Iceland Basin. The Neogene channel floor succession predominantly displays a broad sheeted drift geometry. Bottom current scours and channels were apparently inherited from an episode of enhanced bottom current activity in late Oligocene/early Miocene. The late Quaternary channel-floor succession is dominated by distal glaciomarine sediments, derived from the shelf and slope during glacial stages and mostly transported by ice-rafting. Glacigenic debris flows and minor turbidity currents were also active across the slope region. Consequently, the principal channel-floor facies are glacigenic contourites that show extensive bioturbation, rare primary structures, mixed composition and marked grain size variation. These features indicate the important influence of cyclical fluctuations in bottom current velocity throughout both stadial and interstadial or interglacial periods. However, the concentration of sandy contourites, erosive surfaces and top-only contourites during interstadials/interglacials and during phases of marked cooling or warming testify to the significance of climate-control on contourite deposition.

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain, the Celtic shelf and adjacent continental slope

AbstractIn support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach‐face gravels and sands around the shores of the Celtic Sea. Glacial and sea‐level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south‐central Celtic Sea. Relative sea‐levels were lower, and therefore glacio‐isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice‐rafting at a time of high relative sea‐levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley &amp; Sons, Ltd.

New Data on Upper Quaternary Sediments of the Murmansk Rise in the Barents Sea

The detailed study of sections of two boreholes drilled on the Murmansk Rise of the Barents Sea provided new data on lithology, granulometric composition of sediments, and distribution of oxides and some minerals of the heavy fraction. The biostratigraphic subdivision of Upper Quaternary sediments is based on foraminifers. The recovered glaciomarine Quaternary sediments accumulated in marine periglacial environments. Foraminiferal assemblages dominated by Retroelphidium clavatumand Cassidulina reniforme, which reflect extreme (proximal and distal) glaciomarine environments are replaced upward the section by those formed in normal marine environments. The latter are dominated by Nonion labradoricumand Melonis barleeanus.

The Pre-Windermere Interstadial (Late Devensian) raised marine strata of eastern Scotland and their macrofauna: a review

Late Devensian raised marine deposits predating the Windermere Interstadial (c. 13–11 ka BP) are found between the Moray Firth and Berwick. The widely distributed, sparsely fossiliferous Errol Clay Formation of the firths of Forth and Tay was laid down in a high-arctic environment immediately following the retreat of the Late Devensian (Dimlington Stadial) ice. In the Tay Estuary, sedimentation took place under distal glaciomarine to marine conditions at a time when there was a fully marine connection between the Scottish east coast and the then high-arctic Norwegian Sea. On the south shore of the Moray Firth, the similar, but undated Spynie Clay Formation seems to have been laid down in a wholly glaciomarine environment. Part of the macrofauna attributed to the St. Fergus Silt Formation of the NE Scottish coast may have been either misidentified, or is not in situ. The preservation of the fauna and of delicate sedimentary structures indicate that the arctic clays as a whole were laid down rapidly. It is suggested that tidal currents were minimal, and that waves were dampened by sea ice for much of the year. Bones of the ringed seal, Phoca hispida, have been recorded from 12 sites in eastern Scotland. About 40 macrofaunal taxa are present in the Errol Clay Formation, a number similar to that recorded in the Danish Younger Yoldia Clay, which is of comparable age. The faunal nomenclature is updated, and three species ( Cylichna occulta, Retusa obtusa and Lyonsia arenosa) are added to the macrofaunal list for the Errol Clay Formation. Reports of in situ boreal molluscs and of one possibly North American species in the otherwise high-arctic assemblage are not supported by specimens in extant collections. Differential decay of the fauna below the zone of weathering in the Errol Clay Formation may have resulted from early diagenesis. Deposition of the Late Devensian, pre-Windermere Interstadial marine sediments as a whole was probably diachronous, beginning after 15–14 ka BP on the outer coast, but was confined to a short interval (c. 13.5–13 ka BP) at the type site in the Tay Estuary. In the Forth Estuary, the high-arctic marine fauna adjacent to the retreating ice-front may have survived the rapid climatic amelioration (c. 13 ka BP) at the beginning of the Windermere Interstadial (marked by the Main Perth Shoreline) for perhaps a few decades.

Late-glacial and Holocene paleoceanography and sedimentary environments in the St. Anna Trough, Eurasian Arctic Ocean margin

Based on stratigraphical analysis of twelve sediment cores from the Saint Anna Trough, we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the Holocene. Detailed analysis of benthic and planktic foraminiferal fauna, stable oxygen and carbon isotope analysis, lithostratigraphy and radiocarbon dates, are used to reconstruct the following evolution: After the deglaciation of the Saint Anna Trough >13,300 yr B.P. until 9500 yr B.P., the environment was mainly characterised by low biogenic production, carbonate dissolution and deposition of proximal to distal glaciomarine sediments. Intervals with high abundance of the benthic foraminifer Cassidulina teretis, may indicate influx of Atlantic Water at bottom. The transition into the present interglacial started at 9500 yr B.P. reflected by increased production of foraminifera and bivalves. After 8000 yr B.P. there was a marked drop in planktic δ18O followed by a rise in planktic foraminifera and subsequently an increase of C. teretis. These paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in Nordic seas. The early Holocene warming of the Saint Anna Trough were delayed by ca. 2000 years relative to the northeast Nordic seas. Early Holocene sedimentation rates were relatively high (>100 cm/1000 yr), declining drastically after 8000 yr B.P. (<50 cm/1000 yr). This was presumably caused by reduction in winnowing and/or riverine input.