290 research outputs found
Undersjøiske skred i Balsfjorden, Nord-Norge: egenskaper og sammensetning
No full textBatymetridata, høyoppløselige seismisk data samt en sedimentkjerne fra indre Balsfjorden, Troms, nord-Norge, har blitt analysert for å undersøke sedimentasjonsprosesser i løpet av Holocen, med spesiell fokus på undersjøiske rasavsetninger.
Hovedvekt av denne oppgaven ligger på analyse av den 8,67 m lange sedimentkjernen JM11-001-PC. Dette inkluderte beskrivelse av sedimentoverflate og røntgen bilder, måling av fysiske egenskaper (våt-bulk tetthet, P-bølge hastighet, magnetisk susceptibilitet), kjemiske sammensetning (røntgenfluorescensskanning) og kornfordeling.
Basert på resultater av utført multi-proksi analyse, har sedimenter i kjernen blitt inndelt i 5 litologiske enheter og 6 sub-enheter. Disse representerer marin avsetninger og suspensjonutfelling, avbrutt av turbiditter. Tydelige endringer i røntgenfluorescens (XRF) data, det vil si skarpe økninger i Ti/Rb, K/Rb, Si/Al, Fe/Rb og Ca/Fe skiller turbidittavsetninger fra andre sedimenter.
Resultater ble sammenlignet med tidligere seismostratigrafiske studier (Hansen, 1998) og analyser av sedimentkjerner (Forwick, 2001; Forwick & Vorren, 2002). Sistnevnte studie inneholdte blant annet analyser av kjerne JM98-1014-PC, som ble tatt i umiddelbar nærhet av kjerne JM11-001-PC. Denne kjernen inneholdt tre forholdvis store rasavsetninger (debrisstrøm, turbiditter) av tidlig Holocen alder (ca. 9400 – 8825 14 C år før nåtid)
Retarded deglaciation of north-Spitsbergen fjords during the last glacial – an example of bathymetric controls on the dynamics of retreating glaciers
No full textNorth and west Spitsbergen fjords acted as pathways for fast-flowing ice streams during the last glacial (e.g. Ottesen et al., 2005). The deglaciation of west Spitsbergen fjords occurred stepwise and the ice retreat terminated around 11,200 cal. years BP (calendar years before the present; e.g. Forwick & Vorren, 2009, 2011, and references therein; Baeten et al., 2010). However, the deglaciation dynamics and chronology of north Spitsbergen fjords still remain poorly understood.
We present swath-bathymetry, high-resolution seismic data and two sediment cores from the approx. 110 km long, N-S oriented Wijdefjorden-Austfjorden fjord system, the largest fjord system on northern Spitsbergen. The data indicate that – as in the fjords on west Spitsbergen – multiple halts and/or readvances interrupted the retreat of the ice front during the final phase of the last glacial. However, even though the study area and several west Spitsbergen fjords are fed by the same glacier source (the ice field Lomonosovfonna), the final deglaciation of Wijdefjorden-Austfjorden took place after 9300 cal. years BP, i.e. at least approx. 2000 years later than in the west. We assume that the retarded deglaciation in the north is mainly related to the fjord bathymetry, i.e. a more than 35 km wide and up to 60 m high area in the central parts of the study area (approx. 45 km beyond the present fjord head) that acted as pinning point for the grounded glacier. Multiple, relatively large and partly stacked moraine ridges and sediment wedges are suggested to reflected that the ice front retreated slowly across this shallow area and that repeated readvances interrupted this retreat. The absence of larger sediment wedges in the deeper parts between the shallow area and the fjord head may indicate that the final retreat occurred relatively rapid.
References:
Baeten, N.J., Forwick, M., Vogt, C. & Vorren, T.O., 2010. Late Weichselian and Holocene sedimentary environments and glacial activity in Billefjorden, Svalbard. In: Howe, J.A., Austin, W.E.N, Forwick, M. & Paetzel, M. (eds.): Fjord Systems and Archives. Geological Society, London, Special Publication, 344, 207-223.
Forwick, M. & Vorren, T.O., 2009. Late Weichselian and Holocene sedimentary environments and ice rafting in Isfjorden, Spitsbergen. Palaeogeography, Palaeoclimatology, Palaeoecology 280, 258-274.
Forwick, M. & Vorren, T.O., 2011. Stratigraphy and deglaciation of the Isfjorden area, Spitsbergen. Norwegian Journal of Geology 90, 163-179.
Ottesen, D., Dowdeswell, J.A., Rise, L., 2005. Submarine landforms and the reconstruction of fast-flowing ice streams within a large Quaternary ice sheet: The 2500-km-long Norwegian-Svalbard margin (57°-80°N). Geological Society of America Bulletin 117, 1033-1050
Distribution, deposition and impact of tailing disposal on the seafloor in Ranfjorden, northern Norway
No full textThis study is conducted in Ranfjorden in northern Norway with the goal of gaining a better understanding of the interaction between natural and anthropologic sediments within the fjord. Ranfjorden is of interest due to the fact that it has experienced extensive anthropologic impacts over the last 100 years with the submarine tailings placement (STP) of mine tailings ongoing. The analysis of this study uses the combination of 6 Niemistö sediment cores, 10 sediment grabs, swath bathymetry and high resolution seismic data to identify natural and anthropologic sediments and determine how their distribution has impacted the fjord.
The sediment cores were analyzed to determine their physical properties including magnetic susceptibility, geochemical element measurements, grainsize analysis and lithological analysis. The resulting data showed mine tailings sediments to be characterized by a darker red color, higher magnetic susceptibility and Fe/Sum values with low fluctuations in Fe/Sum values. The more natural fjord sediments are characterized by gray colors, lower magnetic susceptibility and Fe/Sum values with higher fluctuations in Fe/Sum values. Using these identifying traits it was shown that the majority of the inner fjord has experience varied levels of impact from the mine tailings, with all the sediment cores showing traces of mine tailings. The mean grainsize of the sampled mine tailings was shown to vary from fine sand to very fine silt.
The fjord slopes surrounding the mine tailings discharge points at the head of the fjord appeared in the swath bathymetry to have experienced extensive erosion in the form of mass movement and gravity flows. This is attributed to the accumulation of finer mine tailings along these slopes due to back flowing estuarine circulation currents. These currents accompanied by the river-induced halocline appear to capture rising sediment plumes in the water column and concentrate them in those areas. The eroded sediments from those slopes combined with coarser mine tailings are carried further out into the fjord by turbidity currents within a larger submarine channel seen on the swath bathymetry and TOPAS seismic profiles. Samples from the channel show sandy tailing deposits consistent with turbidity currents while areas outside the channels show massive layers of finer tailing sediments consistent with sediment plume fallout. Sandy mine tailing sediments transported by turbidity currents were found 17 km from the discharge point. Shallower samples in the same vicinity showed potential evidence of fine tailing sediments from suspension plume settling.
The discharge of large amounts of tailings at shallower depths combined with the hydrological characteristics of the fjord has allowed for the submarine tailing placement (STP) sediments to have spread throughout the inner fjord basin by turbidity currents and suspension plumes
Post-glacial sedimentary processes and slope instabilities off Nordnesfjellet, Lyngenfjorden, northern Norway
No full textThe Lyngen- and Storfjorden system, Troms County, northern Norway, is surrounded by an alpine landscape, partly with steep mountain sides. Parts of the ~700 m high mountain Nordnesfjellet, on the eastern side of the fjord, are currently moving downslope, and could in the event of sudden failure generate tsunami waves which would affect low-lying areas within a larger region.
The main objective of this study is to integrate multi-proxy analyses of five sediment cores, swath bathymetry and high-resolution seismic data from one NNE-SSW oriented basin of Lyngenfjorden, off Nordnesfjellet, with the purpose of reconstructing mass-wasting activity in the past.
The fjord sides in the study area are up to >30o steep and irregular with depressions, escarpments and furrows of various sizes and ‘freshness’. These features are interpreted to be slide scars and gullies, respectively, related to slope failures. The central parts of the up to 270 m deep basin are generally smooth. However, an up to 8 m high step, crossing almost the entire fjord width, defines the northern limit of a relatively irregular seafloor in the southern part of the study area. Furthermore, sediment-lobe areas are visible as undulating seafloor on the western and eastern sides of the basin.
The high-resolution seismic data reveal that the uppermost <12 ms two-way-travel time (~9 m) are composed of acoustically transparent sediments with few, discontinuous reflections. Deposits causing a chaotic reflection pattern underlie this package within the areas of irregular and undulating seafloor, where also several acoustically well stratified sediment blocks (up to ~300 x 300 x 10 m3) are identified. The acoustically chaotic deposits are e.g. debris flows or turbidites, whereas the blocks are either run-out blocks embedded in the debris flows or slide blocks. The mass-transport deposits are stacked together in several complexes which cover and partly erode into glaciomarine sediments. It is assumed that these complexes were deposited during a relatively short period of frequent mass-wasting directly following the last deglaciation of the study area (~10,800 cal. years BP).
Multiple acoustically transparent wedges thinning from the fjord sides towards the fjord axis are identified. These are most probably debris flows or turbidites. One prominent high-amplitude reflection can be traced over an area of > 7.4 x 1.3 km2. It has varying thickness, on-laps the eastern fjord flank, while it thins towards west.
The cored sediment is mostly massive, olive grey mud. However, coarser, partly well sorted, intervals (up to 13 cm) with sharp and partly erosive lower boundaries occur. Well-sorted intervals are suggested to be turbidites. One turbidite was deposited from a high-density turbidity flow between 3026 and 2930 cal. years BP. It correlates with the strongest reflection within the acoustically transparent interval, thus, indicating that it extends over more than 7.4 x 1.3 km2 of the fjord floor. Wood fragments and moss found within the turbidite suggest that the origin of the failure was onshore.
Mass-transport activity was high shortly after the deglaciation, decreased during the mid-Holocene and increased again during the late Holocene. The late Holocene increase in mass wasting might be related to a climatic deterioration
Sedimentære avsetningsmiljøer og deglasiasjonshistorie i Kaldfjorden, Kvaløya, Troms Fylke
No full textMulti-proxy analyser av tre sedimentkjerner som inkluderer litostratigrafi, fysiske egenskaper og XRF kjerne skanning, har sammen med analyser av høyoppløselig seismisk data blitt integrert for å kunne rekonstruere deglasiasjonshistorien og paleo miljøet i Kaldfjorden på Kvaløya, Troms fylke.
I Kaldfjorden er stor-skala batymetrien delt inn i fire hoved-basseng med en sedimentmektighet på opptil 40 m. Bassengene er adskilt av fire terskler med varierende størrelse. Seismostratigrafien avslørte fire hovedenheter med lokale variasjoner i akustisk signatur. Enhetene er i hovedsak akustisk transparente med enkelte interne refleksjoner. Mulige massetransportavsetninger er observert som kaotiske refleksjoner.
Suspensjons-utfall, is-transportert debris, subglasial «cavity infill» og massetransport er de viktigste sedimentære prosessene som regjerte i Kaldfjorden fra starten av deglasiasjonen. Høyt Fe-innhold og magnetisk mottakelighet i de glasimarine sedimentene tyder på høyere terrigen sedimenttilførsel under deglasiasjonen enn gjennom postglasial tid.
En datering på 18 790 kal. år BP indikerer en tidlig start på deglasiasjonen av området og skiller seg i så måte ut sammenlignet med det store fjordsystemet Andfjord-Vågsfjord. Der den siste deglasiasjonen trolig startet rundt 17 500 kal. år BP (Vorren & Plassen 2002). Overgangen fra glasimarine forhold til et åpent marint miljø er datert til før 11 230 kal. år BP. Fjorden er karakterisert med høyere sedimentasjonsrate under deglasiasjonen enn tiden etterpå, men er likevel generelt lav sammenlignet med andre nordnorske fjorder (Plassen & Vorren 2002, 2003). Asymmetrisk fordeling av de øverste sedimentlagene indikerer erosjon som følge av et økt bunnstrøms-regime i overgangen til holocen. De postglasiale sedimentene i fjorden er avsatt fra suspensjonsutfall eller som omarbeidet materiale i form av massetransport. Hoved-sedimentkilder i dagens fjord er materiale avsatt fra tilstøtende elver og materiale fraktet til fjorden med havstrømmer
Sedimentære avsetningsmiljøer og deglasiasjonshistorie i Ersfjorden, Kvaløya, Troms fylke.
No full text«Multi-proxy» analyser av tre sedimentkjerneprøver (inkludert litostratigrafi, fysiske egenskaper, kornfordelingsanalyse og XRF skanning) og analyse av høyoppløselige seismiske data ble korrelert for å belyse sedimentasjonsprosesser og rekonstruere deglasiasjonshistorie, samt postglasialt sedimentasjonsmiljø under sen Weichsel og Holocen i Ersfjorden på Kvaløya, nordvest i Troms fylke.
Tre hoved-basseng er separert med hver sin hoved-terskel basert på forenklet batymetrikart og seismisk data. Opptil fire seismiske enheter er definert mellom hver regionale seismiske refleksjon. Underste seismiske enhet S1 er subglasialt materiale og fyller de irregulære bassengene i Ersfjorden. De overliggende seismiske enheter (S2a-proksimalt glasimarint materiale, S2-smeltevanns dominert glasimarint materiale og S2-marine avsetninger) tynnes ut mot fjordmunningen.
Totalt 8 litologiske hovedenheter og 9 underenheter er definert i sedimentkjernene. To dominerende miljø ble definert og tolket til glasimarint- og åpent marint miljø. I tillegg ble det identifisert en «overgangssone» med egenskaper fra begge miljøene. Sedimentasjonsratene er avtagende mot de ytre deler av fjorden, på grunn av større avstand fra tidligere og nåværende hoved-sediment kilder. Generell lav sedimentasjonsrate i marint miljø reflekterer lite sedimenttilførsel.
Suspensjonsavsetning, is-transportert debris og massetransport avsetninger var dominerende sedimentære prosesser under deglasiasjonen. I det marine miljøet ble det identifisert konsentrerte avsetninger med et høyt innhold av skjellmateriale og sand. Dette er tolket til å være dannet som et resultat av «winnowing» - prosess og reflekterer gode leveforhold med tilførsel av næringsrikt vann. Økende trend av magnetisk susceptibilitet og Fe-innhold sentralt i fjorden indikerer trolig mindre karbonatrikt materiale og økt tilførsel av terrigent materiale.
Minimumsalder for oppstart av deglasiasjonen og indikasjon på glasimarint miljø i fjorden er datert til omtrent 18 166 kal. år BP. Minimumsalder for slutten av deglasiasjonen er omtrent 11 565 kal. år BP. Sammenlignet med nabofjorden Kaldfjorden tyder dateringene på en forholdsvis tidlig deglasiasjon og overgang fra glasimarint til marint miljø. Dette er betydelig tidligere enn deglasiasjonen av store fjordsystemer i Nord-Norge, f. eks Andfjorden-Vågsfjorden (Vorren & Plassen, 2002), samt tidligere foreslått deglasiasjon av kontinentalhylla vest for Kvaløya (sammenlignet med Rydningen et al., 2013)
Late Weichselian and Holocene sedimentary processes and glacier dynamics in Woodfjorden, Bockfjorden and Liefdefjorden, North Spitsbergen
No full textAbstract
Swath bathymetry, high resolution seismic data and sediment cores were analyzed to reconstruct the Late Weichselian and Holocene sedimentary environments and glacier dynamics in Woodfjorden, Bockfjorden and Liefdefjorden, north Spitsbergen.
Mega-scale glacial-lineations provide evidence of fast-flowing grounded ice draining the northwestern parts of the Late Weichselian Svalbard Barents Sea Ice Sheet. Numerous recessional moraines suggest that the deglaciation of the study area occurred stepwise, whereas the deep outer parts of Woodfjorden were deglaciated relatively rapidly (up to ~200 m/yr). The ice fronts retreated slower (~160 m/yr to 50 m/yr) in the shallower middle and inner parts.
Suspension settling, as well as ice-rafting from icebergs and sea-ice, are the dominating sedimentary processes. Ice-rafting becomes of relative higher importance with increasing distance from the fjord heads. Sediment supply from tidewater glaciers has a large influence in Liefdefjorden, suspension settling from glacifluvial runoff is higher in inner Woodfjorden and in Bockfjorden. The core data show a strong correlation of color and geochemical properties so that these proxies can be applied to study the influence of sediment sources on the study area over time. Red and Ca-rich sediments are indicative for sediments derived from Woodfjorden; brownish and Fe-rich sediments are characteristic proxies for sediment from Liefdefjorden.
Enhanced ice-rafting and dominant sediment delivery from Woodfjorden occurred between ~13,350 and ~13,200 cal. yr. BP. This was followed by an increase in sediment supply from Liefdefjorden until ~12,800 cal. yr. BP. Decreasing ice-rafting, likely related to increased sea-ice cover and cooler surface conditions, occurred from ~12,800 to 12,100 cal. yr. BP. This might be related to climatic cooling during the Younger Dryas. A peak in IRD around ~10,000 cal. yr. BP is inferred to indicate the final phase of deglaciation in Woodfjorden. Increases in ice-rafting from icebergs and sea-ice between ~6200 and ~5000 cal. yr. BP are probably related to a regional cooling. Reduced ice rafting occurred repeatedly during the last ~4000 years, most probably related to the ongoing cooling. The sediment derived mainly from Liefdefjorden. However, periods of enhanced ice-rafting occurred repeatedly until ~1500 cal
Deposits and processes on the tide-influenced fjord-head delta in Dicksonfjorden, Svalbard
No full textThis study investigates for the first time the tide-influenced fjord-head delta in Dicksonfjorden, a fjord in central Spitsbergen, Svalbard. In order to examine the deposits and processes, sediment cores, surface observations and bulk samples have been obtained. Sedimentary facies, log transects and composite logs are presented. Sediment cores are dated with the 210Pb dating method to provide an average sedimentation rate for the intertidal zone. High-resolution aerial images are used to produce a geomorphological map of the area. Landforms and surface features are identified, described and interpreted. Sedimentological trends of the delta are described and interpreted. An aerial photo from 1938 is used to describe and discuss the development of the delta.
Tidal flats, tidal channel, tidal bars, rill channels and cheniers are identified. 7 facies are identified which belong to tidal flat deposits or tidal bar deposits. The tidal flat deposits generally consist of muddy and sometimes sandy laminations, indicating mostly deposition from suspension during high tide. Deformational structures are common and together with circular depressions on the tidal flats they indicate shore ice influence. The tidal bar deposits generally consist of cross-laminated and structureless sand, indicating rapid deposition from a relatively strong heavy sediment-laden current. Heterolithic horizontal laminations, bedforms, reactivation surfaces and desiccation cracks together serve as a strong indicator of tidal influence. The wave-protected setting in which the delta is situated allows a microtidal range to be sufficient for influencing the deposits. Tidal flat deposits transition from mud flat to mixed sand-mud flats moving in a channel-ward direction, indicating a decrease of tidal current speed due to friction against the tidal flat. 210Pb profiles indicate non-steady deposition in the intertidal zone and an average sediment accumulation rate of 0,3 cm/year during the last century. Rill channels develop on tidal flats due to erosion by ebb tide and their distribution can therefor be used to determine the boundary between the intertidal and supratidal zone. Grain-sizes increasing towards the outskirts of the delta indicate a sediment input coming from the surrounding mountains, in addition to Dicksonelva. Because of this and the lack of sand flat deposits in the channel proximal areas of the tidal flats, the delta does not show a good correlation with the previously published facies model from Dalrymple (1992). The aerial photo from 1938 reveals that major tidal channels are located at approximately the same positions as today, indicating that the channel system is quite stable. This is probably linked to the cohesive properties of the muddy tidal flat deposits. Due to relative sea level fall since the last glaciation, the delta represents a forced regressive deposit. The forced regression causes the supratidal part of the delta to slowly increase. Fluvial downcutting and transport of older deposits out on the delta front and slope is likely to be occurring
Unraveling the Chukchi Shelf sediments: insights into past ice sheet extent and gas migration
No full textMarine geophysical methods are utilized to image sedimentary deposits on shelf areas and continental slopes, offering insights into permafrost existence, gas migration, and the historical dynamics of ice sheets. This study focuses on the depositional history of outer Chukchi Shelf sediments and adjacent Chukchi Borderland, investigating glacial periods' impact on the sea floor, specifically a potential ice sheet along the Beringia continental margin. Reprocessed seismic data from 2011, part of a tectonic study on the Chukchi Shelf, reveals a glacial unconformity and distinctive seafloor structures indicative of multiple ice masses. Along the Beringian margin, varying thicknesses of glacial deposits, reaching 450m in certain areas, hint at the extent of an ice sheet and ice stream dynamics. Additionally, seismic data highlights migration structures of rising methane, suggesting its release into the water column, though typical gas seepage surface features are absent. The absence of large-scale marine permafrost on the Chukchi Shelf is indicated by seismic velocities. Overall, these findings provide crucial information for further geological exploration of this previously understudied continental margin, shedding light on its glacial history and potential methane outgassing
Landform assemblages in inner Kongsfjorden, Svalbard: evidence of recent glacial (surge) activity
No full textSwath bathymetry and chirp data have been used to investigate the submarine landform assemblages in inner Kongsfjorden, Svalbard, to reconstruct glacial dynamics during the Late Holocene. Multiple sets of landforms include two types of glacial lineations (groove-ridge features and small, drumlinoid ridges), terminal moraines and associated debris lobes, as well as small push moraines, and indicate repeated surge activity during the last 150 years for four of the five tidewater glaciers terminating in inner Kongsfjorden. Aside from confirming previously documented surges of Kronebreen in 1869, of Kongsvegen, in 1948, and of Blomstrandbreen in 1960, the local bathymetry also indicates a surge of Kongsbreen in 1897, a glacier that has so far been regarded as a non-surge type glacier.
A conceptual model was developed to summarize the surge-induced landform assemblages in Kongsfjorden, and to compare them with other models from terrestrial and marine settings. Striking similarities exist between the Kongsfjorden model and landform assemblages documented for other Spitsbergen fjords. However, eskers and crevasse-fill ridges, the latter thought to be the only landform certainly indicative of glacier surges, lack in Kongsfjorden. Furthermore, the small, drumlinoid ridges inferred to be suggestive of the past ice flow direction in the study area seem to have more in common with glacial lineations generated by surging glaciers on land.
The acoustic data was supplemented with two sediment cores from Kongsfjorden’s innermost basin. The reworked glacimarine deposits at the base of the more proximal core reflect proximal conditions, as they are part of a debris lobe that formed on the distal flank of the terminal moraine deposited during the 1948 surge of Kongsvegen. The stratified muds from the second core contain varying amounts of clasts and also occur on top of the debris lobe. They reveal a relatively distal glacimarine environment mainly influenced by suspension settling from turbid meltwater emanating from Kronebreen or Kongsvegen. Geochemical fluctuations indicate temporal variations in the sediment supply from the two glaciers after 1948.
The few landforms in the outer parts of the study area suggest glacial activity unrelated to the glacier surges. Together with the landforms previously documented from outer Kongsfjorden and its adjacent trough (Kongsfjordrenna), the mega-scale glacial lineations in the outer part of the study area indicate part of a landform assemblage deposited from a fast-flowing ice stream during the Last Glacial Maximum.
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