scholarly journals Cenozoic tectonics of the Western Approaches Channel basins and its control of local drainage systems

2011 ◽  
Vol 182 (5) ◽  
pp. 451-463 ◽  
Author(s):  
Pascal Le Roy ◽  
Claire Gracia-Garay ◽  
Pol Guennoc ◽  
Jean-François Bourillet ◽  
Jean-Yves Reynaud ◽  
...  
Keyword(s):  
Sea Level ◽  
Structural Control ◽  
Drainage Basin ◽  
Sedimentary Cover ◽  
Outer Shelf ◽  
English Channel ◽  
The North ◽  
Tectonic Inversion ◽  
Two Stages ◽  
Tectonic Movements

Abstract The geology of the Channel Western Approaches is a key to understand the post-rift evolution of the NW European continental margin in relation with the Europe/Africa collision. Despite considerable evidence of Tertiary tectonic inversion throughout the Channel basin, the structures and amplitudes of the tectonic movements remain poorly documented across the French sector of the Western Approaches. The effect of the tectonic inversion for the evolution of the “Channel River”, the major system that flowed into the English Channel during the Plio-Quaternary eustatic lowstands, also needs to be clarified. Its drainage basin was larger than the present-day English Channel and constituted the source of terrigenous fluxes of the Armorican and Celtic deep sea fans. A lack of high-resolution seismic data motivated the implementation of the GEOMOC and GEOBREST cruises, whose main results are presented in this paper. The new observations highlight the diachronism and the contrast in amplitudes of the deformations involved in the inversion of the French Western Approaches. The tectonic inversion can be described in two stages: a paroxysmal Paleogene stage including two episodes, Eocene (probably Ypresian) and Oligocene, and a more moderate Neogene stage subdivided into Miocene and Pliocene episodes, driven by the reactivation of the same faults. The deformations along the North Iroise fault (NIF) located at the termination of the Medio-Manche fault produced forced folds in the sedimentary cover above the deeper faults. The tectonic inversion generated uplift of about 700 m of the mid-continental shelf south of the NIF. The isochron map of the reflectors bounding the identified seismic sequences clearly demonstrates a major structural control on the geometry of the Neogene deposits. First, the uplift of the eastern part of the Iroise basin during the upper Miocene favoured the onset of a broad submarine delta system that developed towards the subsiding NW outer shelf. The later evolution of the ’palaeovalley’ network corresponding to the western termination of the “Channel River” exhibits a ’bayonet’ pattern marked by a zigzagging pattern of valleys, with alternating segments orientated N040oE and N070oE, controlled by Neogene faulting. The palaeovalley network could have begun during Reurevian or Pre-Tiglian sea-level lowstands, which exposed the entire shelf below the shelf edge. The amplitude of the sea-level fall is assumed to have been magnified by uplift of the Iroise basin, followed by later tilting of the outer shelf, as observed in many other examples documented along the North Atlantic margins.

scholarly journals NEED Northern European Enclosure Dam

2021 ◽  
Vol 52 (2) ◽  
pp. 6-6
Author(s):  
Sjoerd Groeskamp ◽  
Joakim Kjellsson
Keyword(s):  
Atlantic Ocean ◽  
Sea Level Rise ◽  
Sea Level ◽  
North Sea ◽  
European Countries ◽  
English Channel ◽  
The North ◽  
Northern European ◽  
The North Sea

To protect fifteen northern European countries against sea level rise, a highly ambitious plan was put forward to build massive sea dams across the North Sea and the English Channel, which will cut off the North Sea from the rest of the Atlantic Ocean.

Customs and Traditions of the Isle of Portland Dorset

Antiquity ◽  
1949 ◽  
Vol 23 (91) ◽  
pp. 140-152
Author(s):  
Robert Douch
Keyword(s):  
Sea Level ◽  
Maximum Height ◽  
English Channel ◽  
Maximum Width ◽  
The North ◽  
Solid Block

The Isle of Portland reaches out into the waters of the English Channel. Almost a solid block of stone, it is the most southerly point on the Dorset coast. Its greatest length from north to south is four miles and its maximum width one and a half miles, while its entire circumference is less than nine miles. The north of the island is low-lying, but half a mile inland the ground rises steeply to a maximum height of 496 feet above sea-level at the Verne. From here it slopes away gradually to the southern tip or Bill, 20 feet above sea-level. There has never been a town of Portland and the chief centres of population were originally eight hamlets. Today, three of these, Castletown, Fortuneswell and Chesil have merged to form the main settlement in the north or Underhill, as the district is called, On Tophill three more of the hamlets, Reforne, Easton and Wakeham have similarly run together. Weston and Southwell remain hamlets, while another settlement has grown up around the prison at ‘The Grove’.The ‘Island’ is, in fact, joined to the mainland by the Chesil Beach. But since this pebble bank extends westwards for ten miles before it meets the Dorset coast at Abbotsbury and could be used as a thoroughfare only with the greatest difficulty, the term ‘island’ is no real misnomer. Between Portland and the immediate mainland to the north runs the Fleet, a narrow arm of the sea, wide enough to make the approach across Smallmouth by ferry, before the building of the modern bridge, awkward and, at times, dangerous.

Seismic observation in the eastern Atlantic, 1952

1954 ◽  
Vol 222 (1150) ◽  
pp. 348-356 ◽  
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Deep Sea ◽  
Sedimentary Cover ◽  
Seismic Refraction ◽  
English Channel ◽  
Basaltic Rocks ◽  
Basement Rocks ◽  
Mohorovičić Discontinuity ◽  
Sedimentary Layer

The seismic refraction shooting experiments undertaken in the eastern Atlantic and on the neighbouring continental shelf are briefly described, and the results compared with previous work. The deep-sea results show that basaltic rocks lie immediately below the sedimentary layer, which is variable in thickness, with a mean of about 1 km. The basaltic rocks extend to the Mohorovičic discontinuity at a depth of between 9 and 13 km below sea-level. The results from the stations on the continental shelf at the mouth of the English Channel confirm that the basement rocks slope gently seaward; the value of this slope and the nature of the sedimentary cover vary with position.

The flow of water through the straits of Dover, related to wind and differences in sea level

1956 ◽  
Vol 248 (953) ◽  
pp. 517-551 ◽  
Keyword(s):  
Steady State ◽  
Sea Level ◽  
North Sea ◽  
Sea Water ◽  
Tidal Currents ◽  
English Channel ◽  
Mean Flow ◽  
North East ◽  
The North ◽  
The Difference

The difference in electric potential between the water on opposite sides of the English Channel, as recorded on a telephone cable running from St Margaret’s Bay to Sangatte, has been used to measure the mean flow of water through the Straits of Dover. The records were calibrated by means of the tidal currents, which were know from previous measurements. A p.d. of 1 V corresponds to a current of about 140 cm /s (2.75 knots), the exact calibration depending on the electrical conductivity o f the sea water and having a seasonal variation. Continuous records were obtained during the 15-month period from February 1953 to June 1954. For 4 months, from November 1953 to March 1954, similar records were also obtained on an other cable, crossing the southern North Sea from Aldeburgh to Domburg. Fluctuations due to the Earth currents associated with geomagnetic disturbances occurred from time to time, but did not usually cause any difficulty in in terpretin g the records. The residual flow, after eliminating the tidal currents, has been correlated with the local wind in the Straits and the difference in sea level between the eastern p a rt of the English Channel and the southern part of the North Sea, as determined from tide-gauge records. The tidal currents and elevations were eliminated, approximately, by taking means of 25 hourly readings centred at noon, for each day of the period covered by the observations. The greatest daily rates of flow recorded w ere 79 cm/s (T53 knots) towards the north-east on 1 November 1953 an d 77 cm /s (T49 knots) towards the south-w est on 3 January 1954. F or three periods of un usually strong flow, namely, 19 to 24 September 1953, 26 October to 8 November 1953, and 1 to 6 January 1954, a more detailed analysis was made, eliminating the tidal effects by a method previously used in the analysis of storm surges. The results show the existence of ‘current surges’, the peaks of which lag by up to 6 h behind the corresponding max im a in the wind stress or surface gradient producing them . An attempt has been made to relate the empirical results to the dynamics of flow through the Straits. On the assumption that the 25 h means can be regarded as referring to steady-state conditions, values o f 4-5 x 10<super>-3</super> for the w ind-stress coefficient y<super> 2</super> an d 3-8 x 10<super>-3</super> for the bottom friction coefficient k have been deduced. These rather high values may be due, in part, to the steady-state assumption not being justified. The general features of the current surges are consistent with the dynamical treatment.

Sub-bottom infilled channels in an area of the eastern English Channel

1975 ◽  
Vol 279 (1288) ◽  
pp. 233-241 ◽  
Keyword(s):  
Sea Level ◽  
English Channel ◽  
Hydrographic Data ◽  
Sea Floor ◽  
Fluvial Erosion ◽  
Tidal Regime ◽  
The North ◽  
Sea Bed ◽  
Late Tertiary ◽  
River Valleys

Contouring of geophysical and hydrographic data obtained during a regional geological and geophysical reconnaisance programme has resulted in the discovery of an extensive system of narrow, steep-sided, sub-bottom infilled channels. These channels, which occur to the north of the Cherbourg Peninsula, are, to a certain extent, structurally and stratigraphically controlled by the Cretaceous and Jurassic age strata into which they are cut, and appear to be the remnants of earlier river valleys filled with locally derived bedded and unbedded sands, silts, flints, boulders, clays and gravels. The depth reached by this infilling material is variable, ranging up to 200 m below sea-bed. It is suggested that this system may have originated during late Tertiary (Miocene) and that during the Plio-Pleistocene, when sea level was lower, a combination of tidal scour and fluvial erosion entrenched the system into the exposed sea floor. The present tidal regime and the differing physical characteristics of the strata involved suggest that the present bathymetry is a result of tidal scour

scholarly journals Stratigraphy and depositional evolution of the uppermost Oligocene –Miocene succession in western Denmark

2004 ◽  
Vol 51 ◽  
pp. 89-109 ◽  
Author(s):  
Erik Skovbjerg Rasmussen
Keyword(s):  
Sea Level ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Sediment Supply ◽  
Coarse Grained ◽  
Sea Level Changes ◽  
Fluvial Systems ◽  
North East ◽  
The North ◽  
Tectonic Movements

The uppermost Oligocene – Miocene succession in Denmark is subdivided into six depositional sequences. The development of the succession was controlled both by tectonic movements and eustatic sea-level changes. Tectonic movements generated a topography, which influenced the depositional pattern especially during low sea level. This resulted in sediment by-pass on elevated areas and the confinement of fluvial systems to structural lows. Structural highs further created restricted depositional environments behind the highs during low sea level. The structural highs were also the locus for sandy spit deposits during transgression and high sea level. Initially sediment supply was from the north and north-east but shifted within the Middle Miocene to an easterly direction indicating a significant basin reorganisation at this time. Eustatic sea-level changes mainly controlledthe timing of sequence boundary development and the overall architecture of the sequences.Consequently, the most coarse-grained sediments were deposited within the forced regressive wedge systems tract, the lowstand systems tract and the early transgressive systems tract. The most distinct progradation occurred in the Aquitanian (Lower Miocene) and was associated with a cold period in central Europe.The subsequent rise of sea level until the Serravallian (Middle Miocene) resulted in an overall back-stepping stacking pattern of the sequences and in decreasing incision.

scholarly journals Last Interglacial sea-level data points from Northwest Europe

2021 ◽  
Author(s):  
Kim M. Cohen ◽  
Victor Cartelle ◽  
Robert Barnett ◽  
Freek S. Busschers ◽  
Natasha L. M. Barlow
Keyword(s):  
Sea Level ◽  
Near Field ◽  
Data Entry ◽  
English Channel ◽  
Last Interglacial ◽  
Regional Literature ◽  
The North ◽  
Level Data ◽  
Data Points ◽  
The North Sea

Abstract. Abundant numbers of sites and studies exist that document the Last Interglacial (Eemian, Ipswichian, MIS 5e) coastal record for geographically and geomorphologically diverse NW Europe. This paper documents a database of 141 known Last Interglacial sea-level indicative data points from in and around the North Sea (35 entries in Netherlands, 10 Belgium, 16 in Germany, 17 in Denmark, 8 in Britain) and the English Channel (28 entries for British and 25 for the French side, 3 on the Channel Isles), believed to be a representative and fairly complete inventory and assessment coming from some 80 published sites. The good geographic distribution (some 1500 km SW-NE) across the near field of the Scandinavian and British Ice Sheets and the attention paid to absolute and relative age control are assets of the NW European database compilation. The research history of Last Interglacial coastal environments and sea-level position for this area is long, methodically diverse and spread over regional literature in several languages. Last Interglacial high-stand shorelines of Dutch and German Bight parts of the North Sea, were of lagoonal and estuarine type and have preserved subsurface (data entry included estimates of non-GIA vertical land motion). In contrast, Last Interglacial high-stand shorelines along the English Channel are encountered above modern sea-level (data entry includes datum definitions). Our review and database compilation effort drew from the original regional literature, and paid particular attention to distinguishing between sea-level index points (SLIPs) and marine and terrestrial limiting-points. This paper describes the dominant sea-level indicators produced from region to region, compliant to the database structure of the special issue (WALIS), referenced to original source data. The sea level proxies in majority are obtained from localities with well-developed lithostratigraphic, morpho-stratigraphic and biostratigraphical constraints. Amino-Acid Racemization information is also prominent, especially in Britain, albeit for many sites the older, lesser quality applications of that technique. The majority of European continental sites have chronostratigraphic age-control, notably through regional Pollen Association Zones of known durations. This greatly helps to separate transgression, highstand (‘stillstand’) and regression subsets from within the interglacial, useful when summarizing and/or querying the dataset. In all regions, many SLIPs and limiting points have further independent age-control from luminescence (IRSL, OSL, TL), U-series and ESR dating techniques. Main foreseen usage of this database for the near field region of the European ice sheets is in GIA modelling.

A new hybrid model for filling gaps and forecast in sea level: application to the eastern English Channel and the North Atlantic Sea (western France)

2015 ◽  
Vol 65 (4) ◽  
pp. 509-521 ◽  
Author(s):  
Imen Turki ◽  
Benoit Laignel ◽  
Nabil Kakeh ◽  
Laetitia Chevalier ◽  
Stephane Costa
Keyword(s):  
Sea Level ◽  
Hybrid Model ◽  
North Atlantic ◽  
English Channel ◽  
The North ◽  
The North Atlantic

scholarly journals Transboundary geophysical mapping of geological elements and salinity distribution critical for the assessment of future sea water intrusion in response to sea level rise

2012 ◽  
Vol 16 (7) ◽  
pp. 1845-1862 ◽  
Author(s):  
F. Jørgensen ◽  
W. Scheer ◽  
S. Thomsen ◽  
T. O. Sonnenborg ◽  
K. Hinsby ◽  
...  
Keyword(s):  
Groundwater Flow ◽  
Sea Level Rise ◽  
Sea Level ◽  
Preferential Flow ◽  
Sea Water ◽  
Saline Water ◽  
Seismic Survey ◽  
Salinity Distribution ◽  
Geological Structures ◽  
The North

Abstract. Geophysical techniques are increasingly being used as tools for characterising the subsurface, and they are generally required to develop subsurface models that properly delineate the distribution of aquifers and aquitards, salt/freshwater interfaces, and geological structures that affect groundwater flow. In a study area covering 730 km2 across the border between Germany and Denmark, a combination of an airborne electromagnetic survey (performed with the SkyTEM system), a high-resolution seismic survey and borehole logging has been used in an integrated mapping of important geological, physical and chemical features of the subsurface. The spacing between flight lines is 200–250 m which gives a total of about 3200 line km. About 38 km of seismic lines have been collected. Faults bordering a graben structure, buried tunnel valleys, glaciotectonic thrust complexes, marine clay units, and sand aquifers are all examples of geological structures mapped by the geophysical data that control groundwater flow and to some extent hydrochemistry. Additionally, the data provide an excellent picture of the salinity distribution in the area and thus provide important information on the salt/freshwater boundary and the chemical status of groundwater. Although the westernmost part of the study area along the North Sea coast is saturated with saline water and the TEM data therefore are strongly influenced by the increased electrical conductivity there, buried valleys and other geological elements are still revealed. The mapped salinity distribution indicates preferential flow paths through and along specific geological structures within the area. The effects of a future sea level rise on the groundwater system and groundwater chemistry are discussed with special emphasis on the importance of knowing the existence, distribution and geometry of the mapped geological elements, and their control on the groundwater salinity distribution is assessed.

A review of the tectonics of the northern Middle East region

1984 ◽  
Vol 121 (6) ◽  
pp. 577-587 ◽  
Author(s):  
P. E. R. Lovelock
Keyword(s):  
Late Cretaceous ◽  
Kinematic Model ◽  
Continental Collision ◽  
Dead Sea ◽  
Plate Motion ◽  
Arabian Plate ◽  
Southern Boundary ◽  
The North ◽  
The Dead ◽  
Two Stages

AbstractThe structure of the northern part of the Arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region. The Palmyra and Sinjar zones share a common history of development involving two stages of rifting, one in the Triassic–Jurassic and the other during late Cretaceous to early Tertiary times. Deformation of the Palmyra zone during the Mio-Pliocene is attributed to north–south compression on the eastern block of the Dead Sea transcurrent system which occurred after continental collision in the north in southeast Turkey. The asymmetry of the Palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow Triassic evaporites. An important NW-SE cross-plate shear zone has been identified, which can be traced for 600 km and which controls the course of the River Euphrates over long distances in Syria and Iraq. Transcurrent motion along this zone resulted in the formation of narrow grabens during the late Cretaceous which were compressed during the Mio-Pliocene. To a large extent, present day structures in the region result from compressional reactivation of old lineaments within the Arabian plate by the transcurrent motion of the Dead Sea fault zone and subsequent continental collision.

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