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1
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Online Resource
Hikurangi Plateau: crustal structure, rifted formation, and Gondwana subduction history (2008)
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In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 7, 1525-2027
In: volume:9
In: year:2008
In: number:7
In: extent:31
Description / Table of Contents: Seismic reflection profiles across the Hikurangi Plateau Large Igneous Province and adjacent margins reveal the faulted volcanic basement and overlying Mesozoic-Cenozoic sedimentary units as well as the structure of the paleoconvergent Gondwana margin at the southern plateau limit. The Hikurangi Plateau crust can be traced 50-100 km southward beneath the Chatham Rise where subduction cessation timing and geometry are interpreted to be variable along the margin. A model fit of the Hikurangi Plateau back against the Manihiki Plateau aligns the Manihiki Scarp with the eastern margin of the Rekohu Embayment. Extensional and rotated block faults which formed during the breakup of the combined Manihiki-Hikurangi plateau are interpreted in seismic sections of the Hikurangi Plateau basement. Guyots and ridge-like seamounts which are widely scattered across the Hikurangi Plateau are interpreted to have formed at 99-89 Ma immediately following Hikurangi Plateau jamming of the Gondwana convergent margin at 1̃00 Ma. Volcanism from this period cannot be separately resolved in the seismic reflection data from basement volcanism; hence seamount formation during Manihiki-Hikurangi Plateau emplacement and breakup (125-120 Ma) cannot be ruled out. Seismic reflection data and gravity modeling suggest the 20-Ma-old Hikurangi Plateau choked the Cretaceous Gondwana convergent margin within 5 Ma of entry. Subsequent uplift of the Chatham Rise and slab detachment has led to the deposition of a Mesozoic sedimentary unit that thins from 1̃ km thickness northward across the plateau. The contrast with the present Hikurangi Plateau subduction beneath North Island, New Zealand, suggests a possible buoyancy cutoff range for LIP subduction consistent with earlier modeling.
Type of Medium: Online Resource
Pages: 31
ISSN: 1525-2027
DOI: 10.1029/2007GC001855
Language: English
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  • 2
    Online Resource
    Online Resource
    Terrigenous events and climate history of the Sophia Basin, Arctic Ocean (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 7, 1525-2027
    In: volume:9
    In: year:2008
    In: number:7
    In: extent:14
    Description / Table of Contents: Periods of enhanced terrigenous input to the ocean's basins of the North Atlantic have been reported for the last glacial period. We present a set of new sediment cores recovered from the Sophia Basin north of Svalbard which exhibit widespread ice-rafted debris layers reflecting enhanced terrigenous input throughout the last ~200 ka B.P. Their consistent stratigraphic position, sedimentological character, high sedimentation rate, and geochemical characteristic point to synchronously deposited layers which we name terrigenous input events (TIEs). Owing to their higher densities, they generate excellent reflectors for sediment-penetrating acoustic devices and prominent acoustic layers in the imagery of sedimentary structures. Therefore TIEs can be used for regional acoustic stratigraphy. Each of the events can be linked to major glacial activity on Svalbard. However, the Early Weichselian glaciation is not recorded as a TIE and, in agreement with other work, might not have occurred on Svalbard as a major glacial advance to the shelf break. Nonsynchronous timing of western and northern sources on Svalbard points against sea level-induced iceberg discharge events.
    Type of Medium: Online Resource
    Pages: 14 , graph. Darst
    ISSN: 1525-2027
    DOI: 10.1029/2008GC002038
    Language: English
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  • 3
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    Temperature and stable isotope variations in different water masses from the Alboran Sea (Western Mediterranean) between 250 and 150 ka (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 10, 1525-2027
    In: volume:9
    In: year:2008
    In: number:10
    In: extent:14
    Description / Table of Contents: Mg/Ca, Sr/Ca, and stable isotope measurements have been performed on tests from the planktonic foraminifers Globigerinoides ruber (white), Globigerina bulloides, and Neogloboquadrina pachyderma (right coiling) in samples from Ocean Drilling Program site 977A in the Alboran Sea (Western Mediterranean). The evolution of different water masses between 250 and 150 ka is described. Warm substages were characterized by strong seasonality and thermal stratification of the water column. By contrast, less pronounced seasonality and basin stratification seem to prevail during cold substages. Several periods of stratification due to the low salinity of the upper water mass occurred during the formation of organic-rich layers and also during a possible Heinrich-like event at 220 ka. The three foraminifer species studied show a common and large shell Sr/Ca variability in short timescales, suggesting changes in the global ocean Sr/Ca ratio as one of the main causes of variations in shell composition.
    Type of Medium: Online Resource
    Pages: 14 , graph. Darst
    ISSN: 1525-2027
    DOI: 10.1029/2007GC001906
    Language: English
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  • 4
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    Modification of Ca isotope and trace metal composition of the major matrices involved in shell formation of Mytilus edulis (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 1, 1525-2027
    In: volume:9
    In: year:2008
    In: number:1
    In: extent:8
    Type of Medium: Online Resource
    Pages: 8
    ISSN: 1525-2027
    DOI: 10.1029/2007GC001777
    Language: English
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  • 5
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    Multifrequency geoacoustic imaging of fluid escape structures offshore Costa Rica : Implications for the quantification of seep processes (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 4, 1525-2027
    In: volume:9
    In: year:2008
    In: number:4
    In: extent:16
    Description / Table of Contents: Quantification of fluid fluxes from cold seeps depends on accurate estimates of the spatial validity of flux measurements. These estimates are strongly influenced by the choice of geoacoustic mapping tools. Multibeam bathymetry, side-scan sonar, and Chirp subbottom profiler data of several mound-shaped cold seeps offshore central Costa Rica show great variety in morphology and structure although the features are only a few kilometers apart. Mound 11 (a 35 m high and 1000 m in diameter structure), situated in the SE of the study area, has an irregular morphology but a smooth surface on side-scan sonar data, while mound 12 (30 m high, 600 m across) is a cone of more regular outline but with a rough surface, and mound Grillo (5 m high, 500 m across) shows the same rough surface as mound 12 but without relief. Video observations and sediment cores indicate that the structures are formed by the precipitation of authigenic carbonates and indications for extensive mud extrusion are absent, except for one possible mudflow at mound 11. Different sonar frequencies result in variable estimates of the extent of these mounds with low frequencies suggesting much wider cold seeps, consequently overestimating fluid fluxes. The absence of mud volcanism compared to accretionary prisms where mud volcanism occurs is related to different tectonic styles: strong sediment overpressure and thrust faulting in typical accretionary prisms can generate mud volcanism, while subduction erosion and normal faulting (extension) of the overriding plate at the Costa Rican margin result in fluid venting driven by only slight fluid overpressures.
    Type of Medium: Online Resource
    Pages: 16 , graph. Darst
    ISSN: 1525-2027
    DOI: 10.1029/2007GC001708
    Language: English
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  • 6
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    Online Resource
    Flank collapse and large-scale landsliding in the Cape Verde Islands, off West Africa (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 7, 1525-2027
    In: volume:9
    In: year:2008
    In: number:7
    In: extent:16
    Description / Table of Contents: Large-scale landslides occur on the flanks of many volcanic oceanic islands worldwide. None have taken place in historical time, but their geohazard potential, especially their ability to generate tsunamis, is large. The Cape Verde Islands are a group of 10 large and several smaller volcanic islands off the coast of West Africa between 15 and 17ʿN. A single flank landslide has previously been described from the island of Fogo, but systematic analysis of the Cape Verde group has until now been lacking. This paper describes and interprets a multibeam bathymetry data set covering the slopes of the western Cape Verde Islands, including those of the islands with the most recent volcanic activity, Fogo in the southwest, and Santo Antao in the northwest. All of the larger islands show evidence of large flank landslides, although only Fogo and the southwest part of Santo Antao have failed in the last 400 ka. Tope de Coroa, the volcano at the southwest end of Santo Antao, has been inactive for the past 170 ka and is judged to have a low landslide potential unless volcanic activity resumes. In contrast, there would seem to be a high probability of a future east directed landslide on Fogo, from the area of the highly active Pico do Fogo volcano, although it is impossible to predict a timescale for such an event. A tsunami generated by such a landslide could have a catastrophic effect on the adjacent island of Santiago and possibly even farther afield on the West African coast.
    Type of Medium: Online Resource
    Pages: 16
    ISSN: 1525-2027
    DOI: 10.1029/2008GC001983
    Language: English
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  • 7
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    Online Resource
    Tsunami modeling of a submarine landslide in the Fram Strait (2009)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 10(2009), 4, 1525-2027
    In: volume:10
    In: year:2009
    In: number:4
    In: extent:9
    Description / Table of Contents: The present geological setting west of Svalbard closely parallels the situation off mid-Norway after the last glaciation, when crustal unloading by melting of ice induced very large earthquakes. Today, on the modern Svalbard margin, increasing bottom water temperatures are destabilizing marine gas hydrates, which are held in continental margin sediments consisting of interlayered contourite deposits and glacigenic debris flows. Both unloading earthquakes and hydrate failure have been identified as key factors causing several megalandslides off Norway during early Holocene deglaciation. The most prominent event was the Storegga Slide 8200 years B.P. which caused a tsunami up to 23 m high on the Faroe and Shetland islands. Here we show by numerical tsunami modeling that a smaller submarine landslide west of Svalbard, 100 m high and 130 km wide, would cause a tsunami capable of reaching northwest Europe and threatening coastal areas. A tsunami warning system based on tiltmeters would give a warning time of 1-4 h.
    Type of Medium: Online Resource
    Pages: 9 , graph. Darst
    ISSN: 1525-2027
    DOI: 10.1029/2008GC002292
    Language: English
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  • 8
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    Online Resource
    Reassessing Mg/Ca temperature calibrations of Neogloboquadrina pachyderma (sinistral) using paired Delta 44/40 Ca and Mg/Ca measurements (2009)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 10(2009), 3, 1525-2027
    In: volume:10
    In: year:2009
    In: number:3
    In: extent:14
    Type of Medium: Online Resource
    Pages: 14 , graph. Darst
    ISSN: 1525-2027
    DOI: 10.1029/2008GC002169
    Language: English
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  • 9
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    Interactions between deformation and fluids in the frontal thrust region of the NanTroSEIZE transect offshore the Kii Peninsula, Japan : results from IODP Expedition 316 Sites C0006 and C0007 (2009)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 10(2009), 1525-2027
    In: volume:10
    In: year:2009
    In: extent:14
    Description / Table of Contents: Integrated Ocean Drilling Program (IODP) Expedition 316 Sites C0006 and C0007 examined the deformation front of the Nankai accretionary prism offshore the Kii Peninsula, Japan. In the drilling area, the frontal thrust shows unusual behavior as compared to other regions of the Nankai Trough. Drilling results, integrated with observations from seismic reflection profiles, suggest that the frontal thrust has been active since ~0.78-0.436 Ma and accommodated ~13 to 34% of the estimated plate convergence during that time. The remainder has likely been distributed among out-of-sequence thrusts further landward and/or accommodated through diffuse shortening. Unlike results of previous drilling on the Nankai margin, porosity data provide no indication of undercompaction beneath thrust faults. Furthermore, pore water geochemistry data lack clear indicators of fluid flow from depth. These differences may be related to coarser material with higher permeability or more complex patterns of faulting that could potentially provide more avenues for fluid escape. In turn, fluid pressures may affect deformation. Well-drained, sand-rich material under the frontal thrust could have increased fault strength and helped to maintain a large taper angle near the toe. Recent resumption of normal frontal imbrication is inferred from seismic reflection data. Associated décollement propagation into weaker sediments at depth may help explain evidence for recent slope failures within the frontal thrust region. This evidence consists of seafloor bathymetry, normal faults documented in cores, and low porosities in near surface sediments that suggest removal of overlying material. Overall, results provide insight into the complex interactions between incoming materials, deformation, and fluids in the frontal thrust region.
    Type of Medium: Online Resource
    Pages: 14 , Ill., graph. Darst
    ISSN: 1525-2027
    URL: http://dx.doi.org/10.1029/2009GC002713
    DOI: 10.1029/2009GC002713
    Language: English
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  • 10
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    Online Resource
    Three-dimensional seismic investigations of the Sevastopol mud volcano in correlation to gas/fluid migration pathways and indications for gas hydrate occurrences in the Sorokin Trough (Black Sea) (2008)
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    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 9(2008), 5, 1525-2027
    In: volume:9
    In: year:2008
    In: number:5
    In: extent:22
    Description / Table of Contents: New 3-D seismic investigations carried out across the Sevastopol mud volcano in the Sorokin Trough present 3-D seismic data of a mud volcano in the Black Sea for the first time. The studies allow us to image the complex three-dimensional morphology of a collapse structured mud volcano and to propose an evolution model. The Sevastopol mud volcano is located above a buried diapiric structure with two ridges and controlled by fluid migration along a deep fault system, which developed during the growth of the diapirs in a compressional tectonic system. Overpressured fluids initiated an explosive eruption generating the collapse depression of the Sevastopol mud volcano. Several cones were formed within the depression by subsequent quiet mud extrusions. Although gas hydrates have been recovered at various mud volcanoes in the Sorokin Trough, no gas hydrates were sampled at the Sevastopol mud volcano. A BSR (bottom-simulating reflector) is missing in the seismic data; however, high-amplitude reflections (bright spots) observed above the diapiric ridge near the mud volcano at a relatively constant depth correspond to the approximate depth of the base of the gas hydrate stability zone (BGHSZ). Thus we suggest that gas hydrates are present locally where gas/fluid flow occurs related to mud volcanism, i.e., above the diapir and close to the feeder channel of the mud volcano. Depth variations of the bright spots of up to 200 ms TWT might be caused by temperature variations produced by variable fluid flow.
    Type of Medium: Online Resource
    Pages: 22
    ISSN: 1525-2027
    DOI: 10.1029/2007GC001685
    Language: English
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