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Lomonosov Ridge (lomonosov + ridge)
Selected AbstractsSedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic OceanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010H. Ruth Jackson SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source] The sedimentary structure of the Lomonosov Ridge between 88°N and 80°NGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005Wilfried Jokat SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87°36,N and 80°N perpendicular to and along the LR show a sediment starved continental margin with a variety of geological structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities <3.0 km s,1 are considered to represent Cenozoic sediments deposited after the ridge subsided below sea level. Velocities >4.0 km s,1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155°E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81°N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85°N the seismic data indicate the presence of a bottom simulating reflector along all lines. [source] Towards ground truthing exploration in the central Arctic Ocean: a Cenozoic compaction history from the Lomonosov RidgeBASIN RESEARCH, Issue 2 2010M. O'Regan ABSTRACT The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10,30 m Myr,1) and high permeability values (10,15,10,18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A,C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A,C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean. [source] | ||||||||||