Giant sandstone pipes record basin-scale liquefaction of buried dune sands in the Middle Jurassic of SE Utah

Giant sandstone pipes crop out over a 20 000 km² area of SE Utah. They range from metres to decametres in diameter and crosscut more than 100 m of continental sediments. New and published observations, encompassing all known pipe localities in SE Utah, suggest that the pipes formed by upward movement of groundwater, sand and sediment blocks in response to liquefaction of buried dune sands. Pipe formation was most likely triggered by seismicity during a phase of Cordilleran shortening and regional tectonic reorganization in the late Middle Jurassic. The depth of liquefaction recorded by the pipes far exceeds depths usually considered in earthquake engineering.     

Multi-satellite ocean tide modelling—the K1 constituent

All major ocean tide constituents are aliased into signals with periods less than 90 days from TOPEX/POSEIDON altimetry, except the K₁ constituent. The aliased K₁ has a period of 173 days. Consequently, it might be confounded with height variations caused by the semiannual cycle having a period of 183 days.The correlation between K₁ and the semiannual signal has been investigated both locally and globally using combinations of T/P, ERS-1 and GEOSAT observations. Subsequently, two empirical methods have been investigated to improve the mapping of K₁ from multiple satellites.At high latitudes, where the presence of crossing tracks cannot separate K₁ from the semiannual signal from TOPEX/POSEIDON, the importance of including ERS-1 and GEOSAT observations was demonstrated. A comparison with 29 pelagic and coastal tide gauges in the Southern Ocean south of 50°S gave 5.59 (M₂), 2.27 (S₂) and 5.04 (K₁) cm RMS agreement for FES95.1 ocean tide model. The same comparison for the best empirical estimated constituents based on TOPEX/POSEIDON + ERS-1 + GEOSAT gave 4.32, 2.21, and 4.29 cm for M₂, S₂ and K₁, respectively.     

IMO legislation and its implementation: Accident risk,vessel deficiencies and national administrative practices

The article takes as its point of departure the apparently contradictory findings in recent research about accident rates in shipping and IMO implementation records. It is argued here that although IMO conventions have probably greatly improved shipping safety, they cannot credibly be held to be the chief cause of reduced accident rates as claimed in a recent Marine Policy article, when the documented failures of flag state and port state implementation continue to leave vessels sailing with grave deficiencies. The present analysis posits and corroborates a cluster of linked tendencies that jointly undermine IMO implementation. The core problem is IMO’s weak connection to the national maritime administrations, leading to broadly discretionary practices, exacerbated by language difficulties. Adding new rules is no panacea, as new rules in some cases negatively affect the functioning of existing regulations, and sometimes seem motivated mainly to show political alertness. The structural weakness of the IMO/member state link is the core implementation problem that urgently needs to be dealt with if marine safety is to be improved. The concluding section proposes a reform to bring the IMO out of this conundrum and ensure effective implementation.     

Trends and variability of sea ice in Baffin Bay and Davis Strait, 1953–2001

The extent and duration of sea ice in Baffin Bay and Davis Strait has a major impact on the timing and strength of the marine production along West Greenland. The advance and retreat of the sea ice follows a predictable pattern, with maximum extent typically in March. We examine the area of sea ice in March in three overlapping study regions centred on Disko Bay on the west coast of Greenland. Sea ice concentration estimates derived from satellite passive microwave data are available for the years 1979-2001. We extend the record back in time by digitizing ice charts from the Danish Meteorological Institute, 1953-1981. There is reasonable agreement between the chart data and the satellite data during the three years of overlap: 1979-1981. We find a significant increasing trend in sea ice for the 49-year period (1953-2001) for the study regions that extend into Davis Strait and Baffin Bay. The cyclical nature of the wintertime ice area is also evident, with a period of about 8 to 9 years. Correlation of the winter sea ice concentration with the winter North Atlantic Oscillation (NAO) index shows moderately high values in Baffin Bay. The correlation of ice concentration with the previous winter's NAO is high in Davis Strait and suggests that next winter's ice conditions can be predicted to some extent by this winter's NAO index.     

Marine evidence for climatic instability during the last interglacial in shelf records from northwest Europe

Data from the Greenland ice sheet and continental records from Europe have indicated climatic fluctuations during the last interglacial (Eemian: Oxygen Isotope Substage 5e). Similar fluctuations have not, however, been documented previously from marine environments. Here, we show the existence of two cold events during substage 5e in two marine, benthic foraminiferal, shelf records from northwest Europe and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation.     

Mid-Proterozoic magmatic arc evolution at the southwest margin of the Baltic Shield

Mid-Proterozoic calc-alkaline granitoids from southern Norway, and their extrusive equivalents have been dated by LAM-ICPMS U–Pb on zircons to ages ranging from 1.61 to 1.52 Ga; there are no systematic age differences across potential Precambrian terrane boundaries in the region. U–Pb and Lu–Hf data on detrital zircons from metasedimentary gneisses belonging to the arc association show that these were mainly derived from ca. 1.6 Ga arc-related rocks. They also contain a minor but significant fraction of material derived from (at least) two distinct older (1.7–1.8 Ga) sources; one has a clear continental signature, and the other represents juvenile, depleted mantle-derived material. The former component resided in granitoids of the Transscandinavian Igneous Belt, the other in mafic rocks related to these granites or to the earliest, subduction-related magmatism in the region. Together with published data from south Norway and southwest Sweden, these findings suggest that the western margin of the Baltic Shield was the site of continuous magmatic arc evolution from at least ca 1.66 to 1.50 Ga. Most of the calc-alkaline metaigneous rocks formed in this period show major- and trace-element characteristics of rocks formed in a normal continental margin magmatic arc. The exceptions are the Stora Le-Marstrand belt in Sweden and the Kongsberg complex of Norway, which have an arc-tholeiitic chemical affinity. The new data from south Norway do not justify a suggestion that the crust on the west side of the Oslo Rift had an early to mid-Proterozoic history different from the crust to the east. Instead, they indicate that the different parts of south Norway and southwest Sweden were situated at the margin of the Baltic Shield throughout the mid-Proterozoic. Changes from arc tholeitic to calc-alkaline magmatism reflect changes with time in the subduction zone system, or lateral differences in subduction zone geometry. The NW American Cordillera may be a useful present-day analogue for the tectonomagmatic evolution of the mid-Proterozoic Baltic margin.     

Cretaceous continental margin evolution revealed using quantitative seismic geomorphology,offshore northwest Africa

The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ versus extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Followed by, an Albian‐aged wave‐dominated delta system that prograded to the palaeo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the palaeo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf incised or slope confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km³). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed‐margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source.