Record of large, Late Pleistocene outburst floods preserved in Saanich Inlet sediments, Vancouver Island, Canada

Two anomalous, gray, silty clay beds are present in ODP cores collected from Saanich Inlet, Vancouver Island, British Columbia, Canada. The beds, which date to about 10,500 ¹⁴C yr BP (11,000 calendar years BP), contain Tertiary pollen derived from sedimentary rocks found only in the Fraser Lowland, on the mainland of British Columbia and Washington just east of the Strait of Georgia. Abundant illite-muscovite in the sediments supports a Fraser Lowland provenance.The clay beds are probably distal deposits of huge floods that swept through the Fraser Lowland at the end of the Pleistocene. Muddy overflow plumes from these floods crossed the Strait of Georgia and entered Saanich Inlet, where the sediment settled from suspension and blanketed diatom-rich mud on the fiord floor. The likely source of the floods is Late Pleistocene, ice-dammed lakes in the Fraser and Thompson valleys, which are known to have drained at about the time the floods occurred.     

加拿大不列颠哥伦比亚省温哥华岛纳奈莫群的帆翼龙类化石

An unusual jaw found in a calcite nodule from Collishaw Point, Hornby Island, British Columbia (off the east coast of Vancouver Island) represents the first definitive pterosaur found in British Columbia, and the first istiodactylid from Canada.     

Relative sea-level change inferred from intertidal sediments beneath marshes on Vancouver Island, British Columbia

Relative sea-level change at the time of, and since, the most recent great earthquake at the Cascadia subduction zone is estimated from intertidal sediments at three marshes on western Vancouver Island, British Columbia. We compare the elevation of the pre-earthquake surface, which is marked by a tsunami sand sheet, with the modern depositional elevation range of the sediment type upon which the sand was deposited. At a site south of the Nootka fault zone, which is the northern boundary of the subducting Juan de Fuca plate, tidal mud overlies the pre-earthquake marsh surface. The stratigraphy at this site indicates 0.2–1.6 m of coseismic submergence and 1.1 m of subsequent emergence. In contrast, two sites to the north lack obvious stratigraphic evidence for coseismic land-level change and record between 0.1 and 1.7 m of post-earthquake submergence. These results indicate a difference in tectonic environment across the Nootka fault zone and suggest that plate-boundary rupture during the last great Cascadia earthquake probably did not extend north of central Vancouver Island.     

Distinction between the Storegga tsunami and the holocene marine transgression in coastal basin deposits of western Norway

Many coastal lakes were inundated by both the Storegga tsunami (7000 ¹⁴C yr BP) and the mid-Holocene sea-level rise (the Tapes transgression) in western Norway. The tsunami eroded lake bottoms and deposited graded and/or massive beds of sand, rip-up clasts, and coarse plant material. By contrast, when the rising sea entered the lakes, it deposited only gyttja, silt and fine sand, without causing much erosion of the underlying lake sediments. Storegga tsunami deposits in some coastal lakes were interpreted previously as ordinary marine sediments from the Tapes transgression. Our reinterpretation of these deposits shows that the transgression maximum phase was reached after 6500 yr BP, more than 1000 yr later than previously inferred for the coast of Sunnmøre. The new data cannot be combined in a shoreline diagram without showing the 6000 yr BP and 7000 yr BP shorelines as slightly warped. © 1998 John Wiley & Sons, Ltd.     

Tsunami risk for Western Canada and numerical modelling of the Cascadia fault tsunami

The paper deals with the analysis of tsunami risks for Western Canada and the numerical modelling of a potential tsunami which could affect the region and generate significant damage to the western Canadian coastline. Following a review of the seismic risk and historical tsunamis which occurred along the western Canadian coastline, the authors concluded that this region is highly vulnerable should a major tsunami occur. Consequently, the authors conducted a study on the numerical modelling of a possible tsunami generated by movement along the Cascadia fault, which is located offshore British Columbia. The results of the model outline the significance and extent of the coastal flooding risk associated with such a rare, but destructive phenomenon. The potential for inundation of the low-lying areas around the coastline of Vancouver Island and in and around the City of Vancouver was found to be high. A number of recommendations and conclusions focusing on the results of the numerical simulation are included.     

Sea-level change and paleogeographic reconstructions,southern Vancouver Island,British Columbia,Canada

Forty-eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern Vancouver Island, British Columbia. Sea level fell rapidly from its high stand of about +75 m elevation just before 14 000 cal BP (12 000 radiocarbon yrs BP) to below the present shoreline by 13 200 cal BP (11 400 radiocarbon years BP). The sea fell below its present level 1000 years later in the central Strait of Georgia and 2000 years later in the northern Strait of Georgia, reflecting regional differences in ice sheet retreat and downwasting. Direct observations only constrain the low stand to be below ?11 m and above ?40 m. Analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the Cascadia subduction zone, however, places the low stand at ?30 ± 5 m at about 11 200 cal BP (9800 BP). The inferred low stand for southern Vancouver Island, when compared to the sea-level curve previously derived for the central Strait of Georgia to the northwest, generates differential isostatic depression that is consistent with the expected crustal response between the two regions. Morphologic and sub-bottom features previously interpreted to indicate a low stand of ?50 to ?65 m are re-evaluated and found to be consistent with a low stand of ?30 ± 5 m. Submarine banks in eastern Juan de Fuca Strait were emergent at the time of the low stand, but marine passages persisted between southern Vancouver Island and the mainland. The crustal uplift presently occurring in response to the Late Pleistocene collapse of the southwestern sector of the Cordilleran Ice Sheet amounts to about 0.1 mm/yr. The small glacial isostatic adjustment rate is a consequence of low-viscosity mantle in this tectonically active region.     

Postglacial uplift and relative sea level changes in Finnmark,northern Norway

The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates constrain their chronology. Here we present three Holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of Finnmark; located at the islands Sørøya and Rolvsøya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14,600 cal yr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. Also, the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor. After the Younger Dryas the coast emerged 1.6–1.0 cm per year until about 9500–9000 cal yr BP. Between 9000 and 7000 cal yr BP relative sea level rose 2–4 m and several of the studied lakes became submerged. At the outermost locality Rolvsøya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca 8200–8100 cal yr BP.     

Molluscan biostratigraphy and paleomagnetism of Campanian strata, Queen Charlotte Islands, British Columbia: implications for Pacific coast North America biochronology

A previously uncollected fauna of ammonites, bivalves, and other molluscs, associated with radiolarian microfossils, has been newly recognized near Lawn Hill on the east coast of central Queen Charlotte Islands, British Columbia. The regional biostratigraphic zonation indicates that the Lawn Hill fauna is correlative with the Nostoceras hornbyense zonule of the Pachydiscus suciaensis ammonite biozone, recognized in the Nanaimo Group of southeast Vancouver Island. The Nostoceras hornbyense Zone (new) is herein proposed for strata of Pacific coast Canada containing the zonal index. Several molluscan taxa present in the Lawn Hill section are new to British Columbia and the ammonite fauna suggests that the Nostoceras hornbyense Zone is late Campanian in age, supported by radiolarian taxa present in the section. Strata sampled in the Lawn Hill section preserve reversed-polarity magnetization, considered likely correlative with Chron 32r. The presence of the Nostoceras hornbyense Zone on Queen Charlotte Islands is the first recognition of this zone in Canada north of central Vancouver Island and represents the youngest Cretaceous known in this region. Campanian radiolarians identified from the Lawn Hill section are also the first recognized from the Pacific coast of Canada.     

Mid-Holocene Glacier Peak and Mount St. Helens We Tephra Layers Detected in Lake Sediments from Southern British Columbia Using High-Resolution Techniques

A Glacier Peak tephra has been found in the mid-Holocene sediment records of two subalpine lakes, Frozen Lake in the southern Coast Mountains and Mount Barr Cirque Lake in the North Cascade Mountains of British Columbia, Canada. The age–depth relationship for each lake suggests an age of 5000–5080 ¹⁴C yr B.P. (5500–5900 cal yr B.P.) for the eruption which closely approximates the estimated age (5100–5500 ¹⁴C yr B.P.) of the Dusty Creek tephra assemblage found near Glacier Peak. The tephra layer, which has not been reported previously from distal sites and was not readily visible in the sediments, was located using contiguous sampling, magnetic susceptibility measurements, wet sieving, and light microscopy. The composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid-Holocene tephra layer. Using the same methods, the A.D. 1481–1482 Mount St. Helens We tephra layer was identified in sediments from Dog Lake in southeastern British Columbia, suggesting the plume drifted further north than previously thought. This high-resolution method for identifying tephra layers in lake sediments, which has worldwide application in tephrachronologic/paleoenvironmental studies, has furthered our knowledge of the timing and airfall distribution of Holocene tephras from two important Cascade volcanoes.     

Postglacial sediment yield to Chilliwack Lake,British Columbia,Canada

Tunnicliffe, J., Church, M. & Enkin, R. J. 2012 (January): Postglacial sediment yield to Chilliwack Lake, British Columbia, Canada. Boreas, Vol. 41, pp. 84–101. 10.1111/j.1502‐3885.2011.00219.x. ISSN 0300‐9483. Seismic records and evidence from sediment cores at Chilliwack Lake provide the basis for a long‐term (postglacial) sediment budget for a 324‐km² Cordilleran catchment. Chilliwack Lake (11.8 km² surface area), situated in the North Cascade Mountains, near Chilliwack, British Columbia, was formed behind a valley‐wide recessional moraine in the final phase of post‐Fraser alpine glaciation. Seismic surveys highlight the postglacial lacustrine record, which is underlain by a thick layer of sediments related to deglacial sedimentation. Sediment cores provide details of grain‐size fining from the delta to the distal lake basin. The cores also show a record of intermittent fire and debris flows. Magnetic measurements of lake sediments provide information on grain size, as well as a dating framework. The total postglacial lake‐floor deposit volume is estimated to be 397 ± 27 × 10⁶ m³. Including estimates of fan and delta deposition, the specific postglacial yield to the lake is calculated to be ～86 ± 13 Mg km² a^?1. The sediment volume in the uppermost (Holocene) lacustrine layer is 128 ± 9 × 10⁶ m³, representing ～41 ± 4 Mg km² a^?1 in the Holocene. Compared with other Cordilleran lakes of similar size, particularly those with glacial cover in the watershed, Chilliwack Lake has experienced relatively modest rates of sediment accumulation. This study provides an important contribution to a growing database of long‐term (postglacial) sediment yield data for major Cordilleran lakes, essential for advancing our understanding of the pace of landscape evolution in formerly glaciated mountainous regions.     

Palaeoecology of two lake basins from Disko,West Greenland

The macrofossils, lithology and chronology of two lake basins on Disko in central West Greenland have been investigated. Both lakes were isolated from the sea in the mid-Holocene as a result of relative land uplift. A marine-brackish-limnic sequence was recovered from the Qivittut Lake. The marine fauna is unusually diverse, whereas the brackish water fauna consists only of few species. Immediately after isolation the lake passed through a short-lived eutrophic phase, after which stable, mesotrophic conditions were established. From the second lake basin, the Fortunebay Lake, only limnic sediments were recovered. This lake record demonstrates that rather stable conditions have persisted since mid-Holocene times. Both lakes show anomalously high accumulation rates.     

A geological record of multiple Pleistocene tsunami inundations in an oceanic island: The case of Maio,Cape Verde

In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78·8 ± 0·9 ka, which overlaps within error with the 73 ± 7 ka age proposed for Fogo volcano's flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (<78 ka) remains undated. In summary, the geological record of Maio exhibits well-preserved evidence of repeated tsunami inundation, reinforcing the notion that tsunami hazard is not so low at volcanic archipelagos featuring prominent and highly-active volcanoes such as in Cape Verde.     

Earthquake shaking probabilities for communities on Vancouver Island,British Columbia,Canada

Comprehensive risk assessments are fundamental to effective emergency management. These assessments need to identify the range of hazards (or perils) an entity is exposed to and quantify the specific threats associated with each of those hazards. While hazard identification is commonly, if not formally, conducted in most circumstances, specific threat analysis is often overlooked for a variety of reasons, one of which is poor communication with subject matter experts. This poor communication is often attributable to an adherence to scientific jargon and missed opportunities to simplify information. In Canada, for example, earthquake hazard calculations have been readily available to engineers and scientists for decades. This hazard information, however, is expressed in terms of peak ground accelerations (PGA) or spectral accelerations (SA) that are foreign concepts to most emergency managers, community decision-makers and the public-at-large. There is, therefore, a need to more clearly, simply and effectively express seismic hazard information to the non-scientific community. This paper provides crustal, sub-crustal and subduction interface earthquake shaking probabilities, expressed as simple percentages for each of 57 locations across Vancouver Island, British Columbia, Canada. Calculations present the likelihood of earthquake shaking on Vancouver Island as the probabilities of exceeding each of three shaking intensity thresholds (“widely felt”; onset of “non-structurally damaging” shaking; and onset of “structurally damaging” shaking) over four timeframes (10, 25, 50 and 100 years). Results are based on the latest Geological Survey of Canada hazard models used for the 2010 national building code and are presented in both tabular and graphic formats. This simplified earthquake hazard information is offered to aid local residents, organizations and governments in understanding and assessing their risk and to encourage and facilitate sound earthquake preparedness funding decisions.     

Numerical modelling of coastal inundation from Cascadia Subduction Zone tsunamis and implications for coastal communities on western Vancouver Island,Canada

Natural Hazards - In the present study, numerical simulations were conducted to estimate the spatio-temporal characteristics of tsunami inundation for municipalities on Vancouver Island, Canada, as...     

Tracking recorded fires using charcoal morphology from the sedimentary sequence of Prosser Lake, British Columbia (Canada)

Quantitative analyses of variations in morphological features of charcoal were undertaken in a ²¹⁰Pb-dated sediment core from Prosser Lake (British Columbia, Canada). Seven morphological types of charcoal were defined by particle shape, major-minor axis ratio, apparent porosity and progradation to unburned material. The distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation-sedimentation to lake sediments. Charcoal morphotypes showed distinct relationships to recorded area burned by fires. Fragile charcoal fragments with highly irregular porosity (termed Type M) displayed the strongest correlation to burned area (r² = 0.51; P = 0.0001) and did not produce any false-positive signal for fires recorded within a radius of 20 km around the lake. We infer that high porosity and low density Type M fragments are aerially transported and directly deposited on the lake, and that the fragility of Type M charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record. We propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type, proximity and transportation-sedimentation processes.     

Regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the Cordilleran Ice Sheet in British Columbia,Canada and northern Washington State,USA

Subglacial landsystems in and around Okanagan Valley, British Columbia, Canada are investigated in order to evaluate landscape development, subglacial hydrology and Cordilleran Ice Sheet dynamics along its southern margin. Major landscape elements include drumlin swarms and tunnel valleys. Drumlins are composed of bedrock, diamicton and glaciofluvial sediments; their form truncates the substrate. Tunnel valleys of various scales (km to 100s km length), incised into bedrock and sediment, exhibit convex longitudinal profiles, and truncate drumlin swarms. Okanagan Valley is the largest tunnel valley in the area and is eroded >300 m below sea level. Over 600 m of Late Wisconsin-age sediments, consisting of a fining-up sequence of cobble gravel, sand and silt fill Okanagan Valley. Landform–substrate relationships, landform associations, and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds. They are best explained by meltwater erosion and deposition during ice sheet underbursts.During the Late-Wisconsin glaciation, Okanagan Valley functioned as part of a subglacial lake spanning multiple connected valleys (few 100s km) of southern British Columbia. Subglacial lake development started either as glaciers advanced over a pre-existing sub-aerial lake (catch lake) or by incremental production and storage of basal meltwater. High geothermal heat flux, geothermal springs and/or subglacial volcanic eruptions contributed to ice melt, and may have triggered, along with priming from supraglacial lakes, subglacial lake drainage. During the underburst(s), sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys. Progressive flow channelization focused flows toward major bedrock valleys. In Okanagan Valley, most of the pre-glacial and early-glacial sediment fill was removed. A fining-up sequence of boulder gravel and sand was deposited during waning stages of the underburst(s) and bedrock drumlins in Okanagan Valley were enhanced or wholly formed by this underburst(s).Subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes. The prevailing conceptual model for growth and decay of the CIS suggests significantly thicker ice in valleys compared to plateaus. Subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner (due to melting and enhanced sliding, with significant transfer of ice toward the ice sheet margin). Subglacial lake drainage may have hastened deglaciation by melting ice, lowering ice-surface elevations, and causing lid fracture. This paper highlights the importance of ice sheet hydrology: its control on ice flow dynamics, distribution and volume in continental ice masses.     

The luminescence dating chronology of a deep core from Bosten Lake (NW China) in arid central Asia reveals lake evolution over the last 220 ka

The lacustrine deposits of lakes in arid central Asia (ACA) potentially record palaeoclimatic changes on orbital and suborbital time scales, but such changes are still poorly understood due to the lack of reliable chronologies. Bosten Lake, the largest freshwater inland lake in China, is located in the southern Tianshan Mountains in central ACA. A 51.6‐m‐deep lacustrine succession was retrieved from the lake and 30 samples from the succession were used for luminescence dating to establish a chronology based on multi‐grain quartz OSL and K‐feldspar post‐IR IRSL (pIRIR₂₉₀) dating. Quartz OSL ages were only used for samples from the upper part of the core. The K‐feldspar luminescence characteristics (dose recovery test, anomalous fading test, first IR stimulation temperature plateau test) are satisfactory and from the relationship amongst the quartz OSL, IR₅₀ and pIRIR₂₉₀ doses we infer that the feldspar signals are likely to be well bleached at deposition. Bacon age‐depth modelling was used to derive a chronology spanning the last c. 220 ka. The chronology, lithology and grain‐size proxy record indicate that Bosten Lake formed at least c. 220 ka ago and that lake levels fluctuated frequently thereafter. A stable deep lake occurred at c. 220, 210–180, c. 165, 70–60, 40–30 and 20–5 ka, while shallow levels occurred at c. 215, 180–165, 100–70, 60–40 and 30–20 ka. Bosten Lake levels decreased by at least ~29 m and possibly the lake even dried up between c. 160 and c. 100 ka. We suggest that the water‐level fluctuations in the lakes of ACA may not respond directly to climatic changes and may be affected by a number of complex factors.     

Sedimentary evidence of prehistoric distant-source tsunamis in the Hawaiian Islands

Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low-lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north-eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon-based age models date sand beds from three sites to ca 700 to 500 cal yr bp , which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands.     

Characteristics of tephra in Holocene lake sediments on King George Island, West Antarctica: implications for deglaciation and paleoenvironment

Several reworked tephra layers in gravity-flow deposits are present in lacustrine core sediments collected from Hotel and Rudy Lakes on King George Island, South Shetland Islands, maritime sub-Antarctica. This study tests the values of tephra for establishing regional tephrochronologies for lakes in ice-covered landscapes in the vicinity of volcanoes. The tephra record is more abundant in a long Hotel Lake core (515 cm long). This study uses volcanic glass samples from five tephra layers of Hotel Lake and from one tephra layer of Rudy Lake. Morphologically, tephras are mixtures of basaltic and pumice shards, both having various degrees of vesicularity. Major element analyses of glass shards reveal that the majority of the glass fragments belong to basic glass (<60 wt% SiO₂), compositionally ranging from basalt to low-silica andesite and subalkaline series medium-K tholeiites, probably sourced from Deception Island located 130 km southwest of King George Island. Less than 20% of tephra belongs to silicic glass and occurs in three tephra horizons E of Hotel Lake. However, source volcano(es) for about 10% of basic tephra and silicic tephra are not readily identified from nearby volcanic centers. Except for the studied tephra in Rudy Lake, all tephra samples in Hotel Lake are not ashfall deposits but reworked and redeposited pyroclasts derived from retreating ice sheet, resulting in the occurrence of geochemically equivalent tephra samples in different tephra horizons. The dating of the studied tephra horizons represents the timing of deglaciation rather than that of volcanic eruptions. The result of this study implies that combined with sedimentological information more chemical criterion is necessary to study tephrochronology and regional correlation and to understand paleoenvironmental changes using tephra.     

First indication of Storegga tsunami deposits from East Greenland

A 2.73 m long sediment sequence from Loon Lake, located at 18 m a.s.l. on outer Geographical Society Ø, East Greenland, was investigated for its chronology and changes in physical and biogeochemical properties, macrofossils, and grain‐size distribution. The predominance of marine fossils throughout the sequence, dated by ¹⁴C AMS to between 8630 and 7535 cal. yr BP, shows that the Loon Lake at that time was a marine basin, which according to existing sea‐level curves was about 15–35 m deep. The sequence mainly consists of fine grained homogeneous sediments, which are interrupted by a 0.72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain‐size distribution and in the physical and biogeochemical properties. According to the radiocarbon dates, this sandy horizon was deposited after 8500–8300 cal. yr BP and is interpreted as originating from the Storegga tsunami. The record from Loon Lake provides the first indication of Storegga tsunami deposits from East Greenland. Copyright © 2006 John Wiley & Sons, Ltd.