7 research outputs found

    Deep‐water sediment transport patterns and basin floor topography in early rift basins: Plio‐Pleistocene syn‐rift of the Corinth Rift, Greece

    Get PDF
    Our current understanding on sedimentary deep‐water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio‐Pleistocene deep‐water sedimentary system (Rethi‐Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep‐water syn‐rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast‐count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone‐dominated sheets, B—conglomerate‐dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone‐dominated broad shallow lobes, F—sandstone‐dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland‐fed Mavro delta, with minor contributions from a transverse system of conglomerate‐dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep‐water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin‐floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large‐scale subaqueous landslides and eventual uplift of the whole fault block

    Palaeoenvironmental reconstruction of Paleocene deposits, Cenozoic Central Basin, Spitsbergen. A palynological investigation, with emphasis on dinoflagellate cysts

    No full text
    During the Paleogene, transcurrent motions between NE Greenland and Svalbard caused the formation of the Central Cenozoic Basin in Spitsbergen. The basin formation resulted in deposition of 7 sedimentary formations that cover Paleocene to Eocene time. This study is based on a drill core from Danzigdalen Svalbard, containing the three Paleocene formations: Firkanten -, Basilika -, and Grumantbyen Formations. This study provides a sedimentological description, coupled with palynological analysis on the Danzigdalen core. Qualitative analysis was limited by the poor preservation state and disappointing numbers of palynomorphs. However, 20 dinoflagellate cyst genera have been described and sporomorphs were divided into major morphological groups. The dinoflagellate cyst assemblages is dominated by the three genera Spiniferites, Cerodinium, and Deflandrea. Changes in the palynomorph assemblages reflect a shifting depositional environment, as well as changes in chemistry and nutrient availability of the water column. The distribution of gonyaulacoid dinoflagellate genera in the three formations, along with sedimentological observations, reflect a shift from a terrestrial and inner neritic environment (Firkanten Fm.) to outer neritic and oceanic environments (Basilika Fm.) and finally a return to inner neritic and shoreface environment (Grumantbyen Fm.). The dominance of peridinioid dinoflagellates in the Basilika Formation suggest that the formation was deposited in a nutrient-enriched brackish to hyposaline environment. Results from palynological analysis, including palynofacies, along with sedimentary observations have been compiled into a sequence stratigraphic framework and reveal two parasequences. The Firkanten Formation constitutes the first transgressive-regressive phase and the Basilika-Grumantbyen Formations the latter. The basin has been affected by a shortage of radiometric dates and palaeontological age determinations have suffered from a lack of useful fossil assemblages. 11 tuff beds have been documented within the studied interval. A single concordant age of 60.29 ± 0.29 has been retrieved from a tuff bed in the Basilika Formation (302.30 – 302.21 m depth in core), giving it a Selandian age. This supports Manum and Throndsen´s (1986) previous age determinations

    Umhverfisbreytingar norðvestur af Svalbarða á Kvartertímabili

    No full text
    In 2005 the piston core JM05-030-PC2 was collected from the northwest continental slope of Svalbard, approx. 100km of the nortwest coast at water depths of 1073m. At the study site, the oceanographic system is dominated by two main currents; the East Greenland Current and the West Spitsbergen Current. The East Greenland Current tranports cold and fresh polar water, and is the main transporter of sea-ice into the Atlantic Ocean. The West Spitsbergen Current is the northernmost limb of the North Atlantic Current, and is the main transporter of heat into the Arctic Ocean. Thus this area is sensitive to changes in oceanographic and climatic conditions. The object was to investigate past environmental and climate changes during the Quaternary Period. To achieve this goal a multi-proxy analyses was performed. The studied interval is from 500cm to 600cm depth in core. The methods used were; Lithological logging, magnetic susceptibility, shear strength analysis, water content and granulometry analysis, IRD (Ice Rafted Detritus) count, as well as foraminifera analyses were applied to the studied interval. The results indicate a colder climate than at present. The studied interval of the core is thought to represent ages from approximately 27,500 cal years BP to 21,250 cal years BP. The oldest part of the studied interval shows evidence of seasonal sea-ice and iceberg melting over the site, while the youngest (top) part of the studied interval is indicative of possible perennial sea-ice cover. A debris flow unit towards the top of the core might indicate peak glaciation of the northwestern Svalbard continental shelf. Down-slope movement of sediments are most active during full glaciation of the shelf area. When compared to previously published data; IRD concentration, lithology, magnetic susceptibility, and the general lack of foraminifera in the top of the core point to a depositional timing of the Last Glacial Maximum.Árið 2005 var stimpil kjarninn JM05-030-PC2 tekinn úr norðvestur landgrunnshlíð Svalbarða á 1073m dýpi. Rannsóknarsvæðið er áhugavert í ljósi þess að þar mætast Austur-Grænlandsstraumurinn og Vestur-Spitsbergenstraumurinn. Austur-Grænlandsstraumurinn flytur kaldan og ferskan sjó og er helsti flutningsstraumur ísjaka til Atlantshafsins. Vestur-Spitsbergenstraumurinn er nyrsta grein Norður-Atlantshafsstraumsins og er helsti varmagjafi Norður-Íshafsins. Má því búast við að breytingar á streymi kaldra og hlýrra hafstrauma séu skráðar í sjávarsetlög á svæðinu. Tilgangur rannsóknarinnar var að afla upplýsinga um loftslags- og umhverfisbreytingar Kvarter tímabilsins á háum breiddargráðum. Rannsökuð voru loftlags- og umhverfisháð gögn úr sjávarsetkjarna JM05-030-PC2. Þær aðferðir sem notaðar voru; jarðlagslýsing, segulviðtaksmælingar, skerstyrksgreining, mæling á vatnsinnihaldi, kornastærðargreining, talning hafísbornra korna, götunga talning og tegundagreining. Lengd kjarna JM05-030-PC2 er 8 m en í þessari rannsókn var dýptarbilið 5-6 m skoðað. Niðurstöðurnar benda til töluvert kaldara loftslags en nú og þróunar frá köldu loftslagi til enn kaldara loftslags. Set á umræddu dýptarbili (500 – 600 cm) er talið hafa sest til fyrir 27,500- til 21,250 árum (kvörðuð ár). Elsti hluti dýptarbilsins (600cm) sýnir vísbendingar um árstíðabundna hafísþulu og ísjaka yfir rannsóknarsvæðinu en yngsti hluti dýptarbilsins (500 cm) bendir til þess að hugsanlega hafi hafís hulið rannsóknarsvæðið allt árið um kring. Ofarlega í kjarnanum er völuberg sem talið er að hafi sest til úr aurskriðu. Við hámark síðasta jökulskeiðs voru aurskriður og eðjustraumar algengir á vestur landgrunnshlíð Svalbarða. Völubergið gæti verið tákn um hámark síðasta jökulskeiðs, þegar jöklar náðu að landgrunnsbrún Svalbarða. Að auki benda niðurstöður úr kornastærðargreiningu, segulviðtaks mælingum og greiningu á götungum og hafísbornu efni til kaldara loftslags og nálægðar jökuls

    Provenance of bentonite layers in the Palaeocene strata of the Central Basin, Svalbard: implications for magmatism and rifting events around the onset of the North Atlantic Igneous Province

    No full text
    A fold-and-thrust belt developed between Greenland and Svalbard during the Palaeogene, with an associated foreland basin forming in what is now Spitsbergen. This Central Basin is comprised of the Van Mijenfjorden Group, a ~2.3 km thick sandstone-shale dominated succession that contains prominent and laterally continuous bentonite layers in the lower formations. These altered tephra layers can be used as stratigraphic markers that connect the basin development with regional explosive volcanism and changes to relative plate motions. We sampled and analysed bentonites from nine borehole cores across the Central Basin. Each layer shows evidence of alteration, with mobile elements such as alkali and alkali earth metals particularly disrupted. However, immobile elements including rare earth elements (REE) and preserved igneous minerals retain a magmatic signature, allowing for comparisons with potential volcanic sources to be made. The majority of bentonites are both evolved and strongly alkaline, with chemical signatures that are much closer to the continental rift events around Ellesmere Island and North Greenland than to the early activity of the North Atlantic Igneous Province (NAIP). There is a clear difference between tephra layers in the mid Palaeocene versus late Palaeocene strata. The early bentonites have a REE signature comparable to the volcanics of the Kap Washington Group exposed in North Greenland. The later bentonites have likely come from volcanic centres in the Nares Strait that are also the source of abundant volcaniclastic sediments in the Judge Daly Promontory, Ellesmere Island. These findings suggest that a mid to late Palaeocene change in locus of volcanic provenance may reflect changes in relative plate motions related to the formation of the West Spitsbergen fold-and-thrust belt and the emplacement of the NAIP. However, the lack of bentonites matching NAIP sources suggests that explosive volcanism was of insufficient magnitude to lead to deposition in the Central Basin at this time

    Deep-Water Syn-rift Stratigraphy as Archives of Early-Mid PleistocenePalaeoenvironmental Signals and Controls on Sediment Delivery

    No full text
    The timing and character of coarse siliciclastic sediment delivered to deep-water environments in active rift basins is governed by the complicated interactions of tectonics, climate, eustasy, hinterland geology, and shelf process regime. The stratigraphic archives of deep-water syn-rift basin-fills provide records of palaeoenvironmental changes (e.g. climate and vegetation) in onshore catchments, particularly where they are connected by narrow shelves. However, a chronostratigraphically constrained record of climatic fluctuations and process responses in the hinterland source area recorded in deep-water deposits is rare. Here, we integrate a fully cored research borehole with outcrop exposures of deep-water syn-rift stratigraphy to reconstruct palaeoenvironmental change within the stratigraphy of the West Xylokastro Fault Block in the Corinth Rift, Greece. We used palaeomagnetic and palynological analyses from borehole core samples to develop a chronostratigraphic and palaeoenvironmental model, which we compare to global records of Early-Mid Pleistocene climate and eustatic change. This framework allows establishment of a chronostratigraphic and palaeoenvironmental context to stratigraphic variability encountered in outcrop and in the borehole. Our results show that the similar to 240 m thick studied succession was deposited from similar to 1.1 to 0.6 Ma across the Early-to Mid-Pleistocene transition. During the Early Pleistocene, obliquity-paced climatic variability is largely coherent with vegetation changes of forest coverage within catchments on the southern margin of the Corinth Rift. Large magnitude, eccentricity-paced cyclicity dominant after the Mid-Pleistocene Transition can alter sediment supply from onshore catchments during the warming stages of severe interglacials where expansion of forest cover may trap sediment within catchments. Conglomeratic grade sediment delivery to the deep-water is enhanced during glacial periods, interpreted to reflect sparse forest cover and large winter storms, and during semi-arid, grassland-dominated interglacial highstands during severe interglacials. Base-level rise during minor interglacials is easily outpaced by high sediment supply and is seldom represented stratigraphically. The study demonstrates the value of integrated palynological and sedimentological studies, whilst applying a conservative approach to interpretation when dealing with sparse palynological records from proximal deep-water stratigraphy. The case study provides conceptual models where climatic and vegetation changes can begin to be incorporated as a key control on sediment flux from onshore drainage basins to deep-water syn-rift successions

    Constraining shifts in North Atlantic plate motions during the Palaeocene by U-Pb dating of Svalbard tephra layers

    No full text
    Radioisotopic dating of volcanic minerals is a powerful method for establishing absolute time constraints in sedimentary basins, which improves our understanding of the chronostratigraphy and evolution of basin processes. The relative plate motions of Greenland, North America, and Eurasia changed several times during the Palaeogene. However, the timing of a key part of this sequence, namely the initiation of compression between Greenland and Svalbard, is currently poorly constrained. The formation of the Central Basin in Spitsbergen is inherently linked to changes in regional plate motions, so an improved chronostratigraphy of the sedimentary sequence is warranted. Here we present U-Pb zircon dates from tephra layers close to the basal unconformity, which yield a weighted-mean 206Pb/238U age of 61.596 ± 0.028 Ma (2σ). We calculate that sustained sedimentation began at ~61.8 Ma in the eastern Central Basin based on a sediment accumulation rate of 71.6 ± 7.6 m/Myr. The timing of basin formation is broadly coeval with depositional changes at the Danian-Selandian boundary around the other margins of Greenland, including the North Sea, implying a common tectonic driving force. Furthermore, these stratigraphic tie points place age constraints on regional plate reorganization events, such as the onset of seafloor spreading in the Labrador Sea

    Deep-Water Syn-rift Stratigraphy as Archives of Early-Mid Pleistocene Palaeoenvironmental Signals and Controls on Sediment Delivery

    Get PDF
    The timing and character of coarse siliciclastic sediment delivered to deep-water environments in active rift basins is governed by the complicated interactions of tectonics, climate, eustasy, hinterland geology, and shelf process regime. The stratigraphic archives of deep-water syn-rift basin-fills provide records of palaeoenvironmental changes (e.g. climate and vegetation) in onshore catchments, particularly where they are connected by narrow shelves. However, a chronostratigraphically constrained record of climatic fluctuations and process responses in the hinterland source area recorded in deep-water deposits is rare. Here, we integrate a fully cored research borehole with outcrop exposures of deep-water syn-rift stratigraphy to reconstruct palaeoenvironmental change within the stratigraphy of the West Xylokastro Fault Block in the Corinth Rift, Greece. We used palaeomagnetic and palynological analyses from borehole core samples to develop a chronostratigraphic and palaeoenvironmental model, which we compare to global records of Early-Mid Pleistocene climate and eustatic change. This framework allows establishment of a chronostratigraphic and palaeoenvironmental context to stratigraphic variability encountered in outcrop and in the borehole. Our results show that the ∼240 m thick studied succession was deposited from ∼1.1 to 0.6 Ma across the Early-to Mid-Pleistocene transition. During the Early Pleistocene, obliquity-paced climatic variability is largely coherent with vegetation changes of forest coverage within catchments on the southern margin of the Corinth Rift. Large magnitude, eccentricity-paced cyclicity dominant after the Mid-Pleistocene Transition can alter sediment supply from onshore catchments during the warming stages of severe interglacials where expansion of forest cover may trap sediment within catchments. Conglomeratic grade sediment delivery to the deep-water is enhanced during glacial periods, interpreted to reflect sparse forest cover and large winter storms, and during semi-arid, grassland-dominated interglacial highstands during severe interglacials. Base-level rise during minor interglacials is easily outpaced by high sediment supply and is seldom represented stratigraphically. The study demonstrates the value of integrated palynological and sedimentological studies, whilst applying a conservative approach to interpretation when dealing with sparse palynological records from proximal deep-water stratigraphy. The case study provides conceptual models where climatic and vegetation changes can begin to be incorporated as a key control on sediment flux from onshore drainage basins to deep-water syn-rift successions
    corecore