Structural evidence of the evolution of fore-arc basins off South America

1977 ◽  
Vol 14 (1) ◽  
pp. 102-116 ◽  
Author(s):  
W. T. Coulbourn ◽  
R. Moberly
Keyword(s):  
South America ◽  
Cross Sections ◽  
Seismic Reflection ◽  
Northern Chile ◽  
Oceanic Plate ◽  
Irregular Structure ◽  
Continental Block ◽  
The Face ◽  
Sediment Cover ◽  
Seismic Reflection Profiles

The continental margin of southern Peru and northern Chile was surveyed during the 1973 and 1974 expeditions of the research vessel Kana Keoki. Seismic reflection profiles reveal three large basins at about 1000 m depth between Mollendo, Peru (17°00′ S) and Iquique, Chile (20°00′ S). Only small basins and discontinuous terraces are seen on profiles crossing the Iquique-to-Antofagasta, Chile (23°30′ S) segment of the continental margin.The structural cross-sections of the basins resemble those of arc-trench gaps. The undeformed uppermost reflectors probably represent turbidites, as evidenced by displaced shallow-water benthic foraminifera and coarse sands in cores. Deeper reflectors are generally inclined land-ward, with dips and deformation increasing in the lower reflectors down to about 1.5 seconds penetration. Seaward convergence of these reflectors indicates a progressive shoreward migration of the axis of maximum sedimentation. If the deeper beds are also turbidites, this axis marks the axis of the sediment trap on the continental slope.The structure is consistent with subduction of an oceanic plate and obduction of a portion of its sediment cover. The imbricate stacking of obducted material is lifting an anticlinal ridge visible in most traverses across the trench side of the basin. The growing ridge is deforming the older sediment trapped in the upperslope basin and shifting the locus of deposition shoreward. The irregular distribution of the basins apparently is a product of culminations and depressions of the surfaces of imbricate fault planes. These undulations may result from the transference of the irregular structure of the oceanic plate to the face of the continental block.

3D reconstructions of fault surfaces and key stratigraphic horizons to define recent tectonic activity in the northern Apennines outer fronts and foredeep (northern Adriatic Sea, Italy)

2020 ◽  
Author(s):  
Yuri Panara ◽  
Francesco Emanuele Maesano ◽  
Roberto Basili ◽  
Giacomo Losi ◽  
Jakub Fedorik ◽  
...  
Keyword(s):  
3D Reconstruction ◽  
Cross Sections ◽  
Seismic Reflection ◽  
Adriatic Sea ◽  
Structural Features ◽  
Data Availability ◽  
Tectonic Activity ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Seismic Reflection Profiles

<p>Fault plane attitude and dimension are important parameters for deriving seismotectonic information or input data for earthquake hazard assessment and in this sense a complete 3D view and characterization of geological and structural elements is essential. However, there is always a trade-off between structural complexity and data availability at the scale of the designed application.</p><p>In the last few years, merging public and confidential seismic reflection profiles and borehole data, were used in order to carry out a 3D reconstruction of fault planes and Plio-Pleistocene stratigraphic horizons in the northern Adriatic Sea, at the front of the northern Apennine fold-and-thrust belt and associated foredeep. The study area straddles the Italian coastline and subsurface data interpretation allowed us to reconstruct the structural setting of both onshore and offshore structures. Although it is known that this area has low rates of active tectonic deformation, it hosts important seismogenic faults associated with instrumental seismicity and historical earthquakes.</p><p>The dense distribution of seismic reflection profiles allowed us to perform an accurate 3D reconstruction of almost 50 fault planes, of different dimensions and order of importance. Their geometrical and structural features helped to define the most recent tectonic phases. To this end, we also mapped several Plio-Pleistocene regional unconformities and integrated them with previously published reconstructions of key horizons.</p><p>In some cases, where further published data were available, it was also possible to perform detailed cross sections whose restoration allowed us to reconstruct the post-Miocene (5.33 Ma) slip-rate history of some important tectonic structures with a detail of ~1 Ma. The 3D geological model revealed several structural features like fault continuity and terminations, level of connectivity, presence of lateral ramps, along strike variations of displacement that could not be fully addressed using cross sections alone.</p>

scholarly journals Spatial Relationships between Pockmarks and Sub-Seabed Gas in Fjordic Settings: Evidence from Loch Linnhe, West Scotland

Geosciences ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 283
Author(s):  
Allan Audsley ◽  
Tom Bradwell ◽  
John Howe ◽  
John Baxter
Keyword(s):  
Water Column ◽  
Seismic Reflection ◽  
Hot Spot ◽  
Geophysical Data ◽  
Spatial Relationships ◽  
Hydrocarbon Gases ◽  
Offshore Industry ◽  
Seismic Reflection Profiles ◽  
Spot Analysis ◽  
Sedimentary Carbon

Sub-seabed gas is commonly associated with seabed depressions known as pockmarks—the main venting sites for hydrocarbon gases to enter the water column. Sub-seabed gas accumulations are characterized by acoustically turbid or opaque zones in seismic reflection profiles, taking the form of gas blankets, curtains or plumes. How the migration of sub-seabed gas relates to the origin and distribution of pockmarks in nearshore and fjordic settings is not well understood. Using marine geophysical data from Loch Linnhe, a Scottish fjord, we show that shallow sub-seabed gas occurs predominantly within glaciomarine facies either as widespread blankets in basins or as isolated pockets. We use geospatial ‘hot-spot’ analysis conducted in ArcGIS to identify clusters of pockmarks and acoustic (sub-seabed) profile interpretation to identify the depth to gas front across the fjord. By combining these analyses, we find that the gas below most pockmarks in Loch Linnhe is between 1.4 m and 20 m deep. We anticipate that this work will help to understand the fate and mobility of sedimentary carbon in fjordic (marine) settings and advise offshore industry on the potential hazards posed by pockmarked seafloor regions even in nearshore settings.

scholarly journals Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 117
Author(s):  
Maria Filomena Loreto ◽  
Camilla Palmiotto ◽  
Filippo Muccini ◽  
Valentina Ferrante ◽  
Nevio Zitellini
Keyword(s):  
Seismic Reflection ◽  
Magnetic Data ◽  
Normal Faults ◽  
Sedimentary Sequence ◽  
Initiation Zone ◽  
Arc Setting ◽  
Seismic Reflection Profiles ◽  
Back Arc ◽  
Flower Structures ◽  
Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

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