Using seismic microfacies to identify tidal sand ridges from high-precision three-dimensional seismic reflection data: An example from Xihu Depression, East China Sea Shelf Basin

In 1986, 1181 km of marine seismic reflection data was collected to 18–20 s of two-way traveltime in the Gulf of St. Lawrence area. The seismic profiles sample all major surface tectono-stratigraphic zones of the Canadian Appalachians. They complement the 1984 deep reflection survey northeast of Newfoundland. Together, the seismic profiles reveal the regional three-dimensional geometry of the orogen.Three lower crustal blocks are distinguished on the seismic data. They are referred to as the Grenville, Central, and Avalon blocks, from west to east. The Grenville block is wedge shaped in section, and its subsurface edge follows the form of the Appalachian structural front. The Grenville block abuts the Central block at mid-crustal to mantle depths. The Avalon block meets the Central block at a steep junction that penetrates the entire crust.Consistent differences in the seismic character of the Moho help identify boundaries of the deep crustal blocks. The Moho signature varies from uniform over extended distances to irregular with abrupt depth changes. In places the Moho is offset by steep reflections that cut the lower crust and upper mantle. In other places, the change in Moho elevation is gradual, with lower crustal reflections following its form. In all three blocks the crust is generally highly reflective, with no distinction between a transparent upper crust and reflective lower crust.In general, Carboniferous and Mesozoic basins crossed by the seismic profiles overlie thinner crust. However, a deep Moho is found at some places beneath the Carboniferous Magdalen Basin.The Grenville block belongs to the Grenville Craton; the Humber Zone is thrust over its dipping southwestern edge. The Dunnage Zone is allochthonous above the opposing Grenville and Central blocks. The Gander Zone may be the surface expression of the Central block or may be allochthonous itself. There is a spatial analogy between the Avalon block and the Avalon Zone. Our profile across the Meguma Zone is too short to seismically distinguish this zone from the Avalon Zone.

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Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

Geological Society London Special Publications ◽

10.1144/sp477.26 ◽

2018 ◽

Vol 477 (1) ◽

pp. 223-240 ◽

Cited By ~ 4

Author(s):

D. M. Hodgson ◽

H. L. Brooks ◽

A. Ortiz-Karpf ◽

Y. Spychala ◽

D. R. Lee ◽

...

Keyword(s):

Seismic Reflection ◽

Three Dimensional ◽

Submarine Landslides ◽

Seismic Reflection Data ◽

Karoo Basin ◽

Reflection Data ◽

Seabed Topography ◽

Flow Evolution ◽

Basal Shear ◽

Process Product

AbstractMany mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides.

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Pleistocene forced regressions and tidal sand ridges in the East China Sea

Marine Geology ◽

10.1016/s0025-3227(02)00446-2 ◽

2002 ◽

Vol 188 (3-4) ◽

pp. 293-315 ◽

Cited By ~ 135

Author(s):

Serge Berné ◽

Pierre Vagner ◽

François Guichard ◽

Gilles Lericolais ◽

Zhenxia Liu ◽

...

Keyword(s):

East China Sea ◽

East China ◽

The East China Sea ◽

China Sea ◽

Sand Ridges ◽

Tidal Sand

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The Sask Craton and Hearne Province margin: seismic reflection studies in the western Trans-Hudson Orogen

Canadian Journal of Earth Sciences ◽

10.1139/e05-026 ◽

2005 ◽

Vol 42 (4) ◽

pp. 403-419 ◽

Cited By ~ 38

Author(s):

Z Hajnal ◽

J Lewry ◽

D White ◽

K Ashton ◽

R Clowes ◽

...

Keyword(s):

Seismic Reflection ◽

Three Dimensional ◽

Three Dimensional Model ◽

Seismic Reflection Data ◽

Reflection Data ◽

Regional Tectonic ◽

Detachment Zone ◽

Tectonic Development ◽

Seismic Images ◽

Basal Detachment

A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the RaeHearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the RaeHearne margin Reindeer zone boundary is established. Several phases of tectonic development, including multistage subduction and continentcontinent collision, are inferred for the western margin of the orogen. A bright, shallow (23.5 s two-way traveltime) band of reflectivity (Wollaston Lake reflector) imaged over ~150 000 km2 area is inferred to be a large post-orogenic mafic intrusion. A highly reflective, well-defined and structurally disturbed Moho discontinuity is mapped throughout the western Trans-Hudson Orogen. The present-day crustal architecture of the western Trans-Hudson Orogen is described in terms of the tectonic evolution within the region.

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