Fault and magmatic interaction within Iceland's western rift over the last 9kyr

We present high-resolution 'Chirp' sub-bottom profiler data from Thingvallavatn, a lake in Iceland's western rift zone. These data are combined with stratigraphic constraints from sediment cores to show that movement on normal faults since 9 ka are temporally correlated with magmatic events, indicating that movements were controlled by episodic dyke intrusion. Sediment depo-centres and the focus of subsidence migrated westwards over 3-4 kyr towards the locus of subsequent brittle failure. We interpret this subsidence as related to dyke intrusion a few km along strike, originating from the Hengill volcanic system, which occurred prior to major dyking, faulting and subsidence within the lake at 1.9 ka

Mud mound / ?diapiric features in the Faroe - Shetland Channel

Various high resolution and conventional multi-channel exploration seismic profiling (1966-2002) at the northern end of the Faroe - Shetland Channel (FSC) have identified several large sea bed mounds with a possible diapiric form, originally named the Pilot Whale Diapirs. Some mounds rise over 70 m above the surrounding sea bed and are 2 - 3 km across. The profiles show that the sea bed examples are just a tiny fraction of more extensive subsurface features, covering more than 2000 km2, with less than 10% disturbing the sea bed. The subsurface features occur principally at two levels with a migration northwestwards from deep to shallow. The seismic profiles identifythe host deposits as part of the thick Neogene to Quaternary sequence infilling much of the FSC. The latter includes the North Sea Fan (up to 1 km thick) comprising extensive debrites and some catastrophically emplaced megaslide debrites, two of which abut the mud mounds. The mounds and related subsurface features display various morphologies and seismic facies, and a range of processes may be involved in their development, including mud volcanism, subsurface injection of soft sediment and diapirism. The features are developed above the crest and NW-flank of a NNE trending symmetrical anticline that is expressed at the stratigraphic level of top Palaeogene lavas and they appear to be broadly aligned with the axial trace of this structure. This anticline appears to have continued developing at least into the Pliocene. Material comprising the mounds and related subsurface features appears to have been derived from the subsurface evacuation hollows developed within the ?Eocene to Miocene succession. The formation of these features is thought to be associated with tectonic compression, overpressuring of older sediments due to rapid loading or fluid release upon diagenesis or some combination, including movement on NW-SE trending lineaments. The location of the mounds above a Cenozoic inversion dome and at the margin of a thick sediment wedge (the North Sea Fan) is similar to the setting of large mud mounds observed offshore Norway

IntCal09 and Marine09 radiocarbon age calibration curves, 0-50,000yeats cal BP

The IntCal04 and Marine04 radiocarbon calibration curves have been updated from 12 cal kBP (cal kBP is here defined as thousands of calibrated years before AD 1950), and extended to 50 cal kBP, utilizing newly available data sets that meet the IntCal Working Group criteria for pristine corals and other carbonates and for quantification of uncertainty in both the 14C and calendar timescales as established in 2002. No change was made to the curves from 0–12 cal kBP. The curves were constructed using a Markov chain Monte Carlo (MCMC) implementation of the random walk model used for IntCal04 and Marine04. The new curves were ratified at the 20th International Radiocarbon Conference in June 2009 and are available in the Supplemental Material at www.radiocarbon.org

True volumes of slope failure estimated from a Quaternary mass-transport deposit in the northern South China Sea

Submarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: a) the volume of sub-seismic turbidites generated during slope failure and b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and ODP/IODP well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is ~1035±64 km3, ~406±28 km3 on the slope and ~629±36 km3 in the ocean basin. The volume of sub-seismic turbidites is ~86 km3 (median value) and the volume of shear compaction is ~100 km3, which are ~8.6% and ~9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide-related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm

Pre-Holocene volcanic ash in sediments near Jan Mayen

Poster presentation at the conference Nordic Geological winter meeting, 11.05.22 - 13.05.22, Reykjavik, Icelan

Abrupt climatic events during the last glacial-interglacial transition in Alaska

Evidence is mounting that abrupt climatic shifts occurred during the last glacial-interglacial transition (LGIT) in the North Atlantic and other regions. However, few high-resolution climatic records of the LGIT exist from the high latitudes of the North Pacific rim. We analyzed lake sediments from southwestern Alaska for biogenic silica, organic carbon, organic nitrogen, diatom assemblages, and compound-specific hydrogen isotopes. Results reveal climatic changes coincident with the Younger Dryas, Intra-Allerod Cold Period, and Pre-Boreal Oscillation. However, major discrepancies exist in the paleoclimate patterns of the Bolling-Allerod interstadial between our data and the GISP2 18O record from Greenland, and causes are uncertain. These data suggest that the North Pacific and North Atlantic experienced similar reversals during climatic warming of the LGIT but that the Bolling-Allerod cooling trend in the GISP2 18O record is probably not a hemispheric or global pattern

Tephrochronology and the late Holocene volcanic and flood history of Eyjafjallajökull, Iceland

The hugely disruptive Eyjafjallajökull eruptions of 2010 AD are well known, but the recent history of the volcano is not, which compromises both Icelandic and international hazard assessments and risk planning. This paper identifies and dates the floods caused by two flank eruptions (the c. 920 AD eruption of the Skerin ridge and 6–7th century AD activity around Miðtungugil) and clarifies understanding of c. 6th century AD central vent eruption. These specific contributions to volcanic history are used to illustrate applications of tephrochronology with widespread relevance: how to date eruptions that generate little tephra, better understand the flood hazards presented by glaciated, mountainous volcanoes and the relationship between long-term patterns of activity in neighbouring volcanoes, in this case Eyjafjallajökull and its close (and much larger) neighbour, the volcano Katla

An updated Weichselian chronostratigraphic framework of the Kongsfjorden Trough Mouth Fan and its implications for the glacial history of Svalbard

The Arctic is a climate-sensitive area, responding rapidly to present changes, but for the past changes, the record is still incomplete. For instance, the Weichselian glacial history of the Svalbard–Barents Sea Ice Sheet (SBIS) has largely been reconstructed based on studies of the fragmentary Spitsbergen terrestrial and shelf records. However, the sediments removed from the land and shelf areas during peak glacials were deposited on trough mouth fans located along the continental slope. By studying the stratigraphy and processes of the trough mouth fans, comprising a more complete sediment archive, our new data have allowed gaps in the Weichselian glacial history of the SBIS to be refined and filled. Here we present new lithological and geochronological data from the Kongsfjorden Trough Mouth Fan, closely linked to the advance and decay of the SBIS. High-resolution TOPAS seismic profiles reveal three distinct packages of glacigenic debris flows (GDFs) within its upper stratigraphy, each interpreted to represent an advance of the SBIS to the shelf edge. A radiocarbon dated, 12.6-m-long core from the southern flank of the Kongsfjorden Trough Mouth Fan penetrates trough sediments directly linked to the youngest GDF package and terminates in the second GDF, allowing us to study the last two Kongsfjorden ice-stream advances in greater detail than was previously possible. The age model of core GS10-164-09PC, based on combining 14C-, 18O-stable isotope and magnetic susceptibility data, spans the last ~54 ka. An Early Weichselian glacial advance is tentatively dated to have ended at ~90 ka. A second peak glaciation is estimated at ~70 ka, followed by a deglaciation from ~54 ka. An ice rafted debris-rich unit (U7) dated between 38 and 34 ka, followed by a plumite (U6), indicates an advance of unknown extent. The Last Glacial Maximum advance is dated to before 24 ka BP, followed by a rapid deglaciation at ~15 ka. The presence of coarser-grained sorted sediments at the present seafloor is attributed to the influence of the West-Spitsbergen Current, acting on water depths of at least 846 m, and is thought to have worked in the vicinity of the coring site since ~14 ka BP.publishedVersio