The architecture and the multi-stage evolution of the North Iberian margin (Bay of Biscay)

2020 ◽  
Author(s):  
Patricia Cadenas ◽  
Gianreto Manatschal ◽  
Gabriela Fernández-Viejo
Keyword(s):  
Rift System ◽  
Plate Boundaries ◽  
Bay Of Biscay ◽  
Velocity Models ◽  
The North ◽  
Rifted Margins ◽  
Multi Stage ◽  
Stratigraphic Architecture ◽  
Half Graben ◽  
Iberian Margin

<p>In this work, we address the problem of the formation and reactivation of multi-stage rifting based on the study of the central North Iberian margin, located at the southern Bay of Biscay triangular oceanic domain. This magma-poor rifted margin registered three major Mesozoic rift events and a subsequent Alpine compressional reactivation, representing a unique setting to study the architecture of a multi-stage rift system and its control on subsequent reactivation. Based on a dense dataset of high quality 2D seismic reflection profiles, boreholes and published velocity models, we define, describe and map structural domains, major extensional and compressional structures, and the depth and thickness of syn-rift units. We provide new structural maps showing the geometry and spatial distribution of major rift basins and bounding structures.</p><p>The analysis of the tectono-stratigraphic architecture led us to define three rift systems. A diffuse and widespread of Triassic age, with classical fault-bounded half-graben basins, a second, narrow, deep and localised Late Jurassic to Barremian transtensional system, and a third, widely distributed Aptian to Cenomanian hyperextended system, including two distinctive domains. Our results show that each rift system controlled successive rift events, and that the stacking and overlap of the three rift systems resulted in a complex and segmented 3D template that guided subsequent compressional reactivation. Compression affected on a distinctive way the three rift systems, leading to an amplification of the margin segmentation.</p><p>This work shows that unravelling the tectono-stratigraphic architecture and evolution of multi-stage rift systems can provide key insights not only to decipher the spatial and temporal evolution of divergent plate boundaries, but also to set up present-day kinematic templates to test dynamic plate deformable models of conjugate rifted margins. It will also be a keystone to constrain early stages of margin reactivation and the architecture of reactivated rifted margins now incorporated in orogenic systems.</p>

Basement-decoupled hyperextension rifting: The tectono-stratigraphic record of the salt-rich Pyrenean necking zone (Arzacq Basin, SW France)

2021 ◽  
Author(s):  
M. Ducoux ◽  
E. Masini ◽  
J. Tugend ◽  
J. Gómez-Romeu ◽  
S. Calassou
Keyword(s):  
Rift System ◽  
Rifted Margins ◽  
Salt Layer ◽  
Stratigraphic Architecture ◽  
Stratigraphic Record ◽  
Half Graben ◽  
Southern Side ◽  
Well Data ◽  
Stratigraphic Evolution ◽  
Sw France

Half grabens and supra-detachment basins correspond to end-member basin types of magma-poor rift settings, each of them showing a characteristic stratigraphic architecture. The occurrence of a basement-cover décollement has been shown to drastically change the stratigraphic architecture of half graben basins, however, the effect of such basement-cover décollement remains to be documented in supra-detachment basins formed during hyper-extension. We investigate the tectono-stratigraphic record of the Arzacq Basin (SW France) recording the formation of a salt-rich Cretaceous hyperextended rift system. Combining 2-D and 3-D seismic reflection calibrated from well data, we show that this basin is an asymmetric syn-rift extensional syncline growing above a pre-kinematic salt layer. By mapping the sub-salt basement, we show that the formation of this syncline is controlled by the South-Arzacq Fault (SAF), soling in the sub-salt basement. Based on crosscutting relationships and the observed southward migration of syn-rift depocenters, this N110°-striking, 20°-dipping structure accommodates >10 km of thick-skinned extension. The overlying supra-salt cover coherently glided, following the basement geometry. The 3-D segmentation of the SAF and the sub-salt stratigraphic architecture of the Arzacq Basin suggest a roughly dip-slip kinematic. A post-kinematic kilometer-scale uplift is documented on the southern side of the Arzacq Basin. It may result from the increasing lithospheric thinning and thermal support at the end of asymmetric hyperextension. As salt commonly occurs in extensional settings, we believe that our description of the tectono-stratigraphic record of a basement-decoupled supra-detachment basin has global applicability to unleash the tectono-stratigraphic evolution of worldwide hyper-extended rifted margins.

Løvehovden fault and Billefjorden rift basin segmentation and development, Spitsbergen, Norway

2010 ◽  
Vol 148 (1) ◽  
pp. 154-170 ◽  
Author(s):  
H. D. MAHER ◽  
A. BRAATHEN
Keyword(s):  
Normal Fault ◽  
Shear Zones ◽  
Rift Basin ◽  
The North ◽  
Structural Style ◽  
Stratigraphic Architecture ◽  
Movement Component ◽  
Half Graben ◽  
Northern Portion ◽  
Local Relief

AbstractThe Carboniferous Billefjorden rift basin is a well-known example of a suite of Carboniferous basins on the Barents Shelf and NE Greenland. The basin has a clastic, carbonate and evaporite fill with complex and disputed stratigraphic relationships, especially regarding the Ebbadalen and Minkinfjellet formations. Geometrically, the basin is considered a simple half-graben. A N–S-trending fault and monocline structure within the northern portion of the basin, the Løvehovden fault, has lithological and thickness differences across it within the Minkinfjellet and possibly Ebbadalen formations. The fault shows W-side-down movement, defining a sub-basin within the larger half-graben. Significant along-strike changes occur. Down-throw to the west is at least 150 metres and possibly 400 metres, as shown by across-fault thickness differences of Ebbadalen and/or Minkinfjellet formations. To the east of the fault, the contact between the Ebbadalen and Minkinfjellet formations is a disconformity with significant local relief, and is interpreted to represent exposure from footwall uplift, and associated near- or at-surface solution, producing basal stratiform breccias. A similar contact is not exposed west of the fault. Monoclinal deformation and thickening of the younger Wordiekammen Formation above and across the monocline constrain a later movement component. Kinematic data and the structural style clearly indicate the Løvehovden fault is a normal fault with associated tri-shear zone development, consistent with the regional Carboniferous rift setting. Earlier interpretations describe the Løvehovden fault and monocline as Tertiary contractional features. In contrast, our work advocates that they are an important architectural basin element, defining a sub-basin within the Billeforden Trough during Minkinfjellet Formation deposition, with insignificant, if any, Tertiary reactivation. The Løvehovden fault is aligned with and represents the southern termination of the Lemströmfjellet fault to the north. Thus, the Billefjorden basin changes from a narrow graben to a broader half-graben to the south. These along-strike changes have important implications for the stratigraphic architecture of the basin, and for palaeogeographic reconstructions. These results and application of 3-D models for extension related tri-shear zones may help inform interpretation of other Carboniferous basins on the Barents Shelf.

Revisiting Hotspots and Continental Breakup – Updating the Classical Three-arm Model

2021 ◽  
Author(s):  
Carol Stein ◽  
Seth Stein ◽  
Molly Gallahue ◽  
Reece Elling
Keyword(s):  
North Atlantic Ocean ◽  
Ocean Basin ◽  
Rift System ◽  
Plate Boundaries ◽  
East African Rift System ◽  
Continental Rifting ◽  
East African ◽  
Continental Breakup ◽  
The North ◽  
Junction Points

<p>In two classic papers, Burke and Dewey (1973) and Dewey and Burke (1974) proposed that continental rifting begins at hotspots - domal uplifts with associated magmatism - from which three rift arms extend. Rift arms from different hotspots link up to form new plate boundaries along which the continent breaks up, generating a new ocean basin and leaving failed arms termed aulacogens within the continent.  In subsequent studies, hotspots became increasingly viewed as manifestations of deeper upwellings or plumes, which were the primary cause of continental rifting. We revisit this conceptual model and find that it remains useful, though some aspects require updates based on subsequent results.  Many three-arm systems identified by Burke and Dewey (1973) are now recognized to be or have been boundaries of transient microplates accommodating motion between diverging major plates. Present-day examples include the East African Rift system and the Sinai microplate.  Older examples include rifts associated with the opening of the South Atlantic in the Mesozoic and the North Atlantic Ocean over the last 200 Ma,  rifts in the southern U.S associated with the breakup of Rodinia, and intracontinental rifts formed within India during the breakup of Gondwanaland. The microplates form as continents break up, and are kinematically distinct from the neighboring plates, in that they move separately. Ultimately, the microplates are incorporated into one of the major plates, leaving identifiable fossil features on land and/or offshore. In many cases the boundaries of microplates during continental breakup are located on preexisting zones of weakness and influenced by pre-existing fabric, including older collisional zones. Hotspots play at most a secondary role in continental breakup, in that most of the associated volcanism reflects plate divergence, so three-arm junction points may not reflect localized upwelling of a deep  mantle plume.</p>

Extensional detachments related to extreme crustal thinning and their fate during contractional reactivation: the Le Danois-North Mauléon offshore-onshore examples in north Iberia

2021 ◽  
Author(s):  
Patricia Cadenas ◽  
Rodolphe Lescoutre ◽  
Gianreto Manatschal
Keyword(s):  
Cross Sections ◽  
Rift System ◽  
Northern Spain ◽  
Crustal Rocks ◽  
Detachment Faults ◽  
The North ◽  
Rifted Margins ◽  
Crustal Thinning ◽  
Seismic Reflection Profiles ◽  
Detachment Faulting

<p>Extensional detachment faults accommodate high degrees of crustal thinning and exhumation, shaping largely the final architecture of magma-poor rifted margins. Great efforts have been directed to study extensional detachments based on offshore seismic surveys and onshore field analogues. However, little is known about the breakaway of these structures as well as their role and evolution during rifting and subsequent contractional reactivation. </p><p>In this work, we use the Le Danois-Labourd offshore-onshore natural laboratory (northern Spain) to explore the features characterising major Mesozoic extensional detachment faults and their fate during subsequent Alpine contractional reactivation. Both sites keep evidence of Mesozoic extensional detachment faulting and high degrees of crustal thinning, including exhumed mid-crustal granulites reworked as clasts into Apto-Albian syn-rift sediments, and show mild Alpine reactivation, corresponding at present-day to structural highs. Relying on the interpretation of high quality 2D seismic reflection profiles offshore and on field-based cross-sections onshore, we describe and compare the former rift architecture associated with these major detachment faults and the distribution of contractional structures at the two sites.</p><p> This combined study enable us to evidence strong structural similarities between the two sites and to propose that the Le Danois and the North Mauléon extensional detachment systems are major rift structures within the North Iberian rift system. We propose that they were responsible for high degrees of crustal thinning and the exhumation of mid-crustal rocks during the Late Aptian to Albian N-S directed extension. Major thrusts truncated the two extensional detachments during subsequent Alpine reactivation, leading to the uplift and tilting of the Le Danois and the Labourd rift-inherited crustal blocks. We suggest that the location of the two blocks at the termination of offset/overlapped hyperextended rift segments allowed for their preservation as mildly inverted structural highs, including rift-related structures.</p>

scholarly journals Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Paraskevi Nomikou ◽  
Dimitris Evangelidis ◽  
Dimitrios Papanikolaou ◽  
Danai Lampridou ◽  
Dimitris Litsas ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Activity ◽  
Volcanic Rocks ◽  
Active Tectonics ◽  
Normal Fault ◽  
Aegean Sea ◽  
Northern Margin ◽  
The North ◽  
Eastern Aegean ◽  
Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

scholarly journals Crustal variability along the rifted/sheared East African margin: a review

2021 ◽  
Vol 41 (2) ◽  
Author(s):  
Maren Vormann ◽  
Wilfried Jokat
Keyword(s):  
East Africa ◽  
Shear Zone ◽  
Structural Changes ◽  
The South ◽  
East African ◽  
The North ◽  
Rifted Margins ◽  
Continental Block ◽  
Seismic Lines ◽  
Southeastern Madagascar

AbstractThe East African margin between the Somali Basin in the north and the Natal Basin in the south formed as a result of the Jurassic/Cretaceous dispersal of Gondwana. While the initial movements between East and West Gondwana left (oblique) rifted margins behind, the subsequent southward drift of East Gondwana from 157 Ma onwards created a major shear zone, the Davie Fracture Zone (DFZ), along East Africa. To document the structural variability of the DFZ, several deep seismic lines were acquired off northern Mozambique. The profiles clearly indicate the structural changes along the shear zone from an elevated continental block in the south (14°–20°S) to non-elevated basement covered by up to 6-km-thick sediments in the north (9°–13°S). Here, we compile the geological/geophysical knowledge of five profiles along East Africa and interpret them in the context of one of the latest kinematic reconstructions. A pre-rift position of the detached continental sliver of the Davie Ridge between Tanzania/Kenya and southeastern Madagascar fits to this kinematic reconstruction without general changes of the rotation poles.

scholarly journals Evidence for strong relations between the upper Tagus loess formation (central Iberia) and the marine atmosphere off the Iberian margin during the last glacial period

2021 ◽  
pp. 1-30
Author(s):  
Daniel Wolf ◽  
Thomas Kolb ◽  
Karolin Ryborz ◽  
Susann Heinrich ◽  
Imke Schäfer ◽  
...  
Keyword(s):  
North Atlantic ◽  
Moisture Transfer ◽  
Sea Temperature ◽  
Last Glacial ◽  
Atmospheric Circulation Patterns ◽  
The North ◽  
Terrestrial Environments ◽  
The North Atlantic ◽  
Iberian Margin ◽  
The Last Glacial

Abstract During glacial times, the North Atlantic region was affected by serious climate changes corresponding to Dansgaard-Oeschger cycles that were linked to dramatic shifts in sea temperature and moisture transfer to the continents. However, considerable efforts are still needed to understand the effects of these shifts on terrestrial environments. In this context, the Iberian Peninsula is particularly interesting because of its close proximity to the North Atlantic, although the Iberian interior lacks paleoenvironmental information so far because suitable archives are rare. Here we provide an accurate impression of the last glacial environmental developments in central Iberia based on comprehensive investigations using the upper Tagus loess record. A multi-proxy approach revealed that phases of loess formation during Marine Isotope Stage (MIS) 2 (and upper MIS 3) were linked to utmost aridity, coldness, and highest wind strengths in line with the most intense Greenland stadials also including Heinrich Events 3–1. Lack of loess deposition during the global last glacial maximum (LGM) suggests milder conditions, which agrees with less-cold sea surface temperatures (SST) off the Iberian margin. Our results demonstrate that geomorphological system behavior in central Iberia is highly sensitive to North Atlantic SST fluctuations, thus enabling us to reconstruct a detailed hydrological model in relation to marine–atmospheric circulation patterns.

Determinacy of fecundity in sole (Solea solea) from the Bristol Channel

1990 ◽  
Vol 70 (4) ◽  
pp. 803-813 ◽  
Author(s):  
J. W. Horwood ◽  
M. Greer Walker
Keyword(s):  
Bay Of Biscay ◽  
English Channel ◽  
Potential Fecundity ◽  
Frequency Distributions ◽  
The North ◽  
Size Frequency ◽  
Solea Solea ◽  
The North Sea ◽  
The Common ◽  
Common Sole

Ovaries of the common sole (Solea solea (Linnaeus)) were collected prior to, or at the beginning of, spawning from the spawning grounds in the Bristol Channel. Size frequency distributions of oocytes over 100 μm are presented. They clearly show a break in the size frequency distributions, at about 170 μm, indicating that the production of new oocytes to be spawned that season had ceased. It indicates that the sole is a determinate spawner and that, at least for this population, an annual potential fecundity can be measured. Estimated annual fecundity at length of Bristol Channel sole is calculated, and values are compared with those found for sole from the North Sea, eastern English Channel and the Bay of Biscay.

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