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. 2017 Apr 4:8:15101.
doi: 10.1038/ncomms15101.

Two-stage opening of the Dover Strait and the origin of island Britain

Sanjeev Gupta  1 , Jenny S Collier  1 , David Garcia-Moreno  2   3 , Francesca Oggioni  1 , Alain Trentesaux  4 , Kris Vanneste  2 , Marc De Batist  3 , Thierry Camelbeeck  2 , Graeme Potter  5 , Brigitte Van Vliet-Lanoë  6 , John C R Arthur  7
Affiliations

Two-stage opening of the Dover Strait and the origin of island Britain

Sanjeev Gupta et al. Nat Commun. .

Abstract

Late Quaternary separation of Britain from mainland Europe is considered to be a consequence of spillover of a large proglacial lake in the Southern North Sea basin. Lake spillover is inferred to have caused breaching of a rock ridge at the Dover Strait, although this hypothesis remains untested. Here we show that opening of the Strait involved at least two major episodes of erosion. Sub-bottom records reveal a remarkable set of sediment-infilled depressions that are deeply incised into bedrock that we interpret as giant plunge pools. These support a model of initial erosion of the Dover Strait by lake overspill, plunge pool erosion by waterfalls and subsequent dam breaching. Cross-cutting of these landforms by a prominent bedrock-eroded valley that is characterized by features associated with catastrophic flooding indicates final breaching of the Strait by high-magnitude flows. These events set-up conditions for island Britain during sea-level highstands and caused large-scale re-routing of NW European drainage.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Sonar bathymetry of the eastern English Channel shelf.
Map showing bathymetry of the eastern English Channel gridded at 30 m cell size. The location of the study area in Fig. 2 is indicated. LC, Lobourg Channel; MPV, Median Palaeovalley; NPV, Northern Palaeovalley. An analysis of the downstream morphology is given in ref. . See Methods for details of offshore bathymetry data. Onshore elevation is from SRTM. Yellow dashed line indicates the axial trace of the Weald–Artois anticline.
Figure 2
Figure 2. Sonar bathymetry of the northeastern English Channel shelf.
(a) Coloured and shaded relief bathymetry compilation map of the Dover Strait region. C, Colbart tidal sand ridge; LC, Lobourg Channel; NPV, Northern Palaeovalley; P, platform; V, Varne tidal sand ridge; SI, streamlined island; TSR, tidal sand ridge. Onshore topography (scale in Fig. 1) shown as coloured shaded relief is from Shuttle Radar Topography Mission (SRTM). Note valley network incised into platform, P, indicating sub-aerial exposure of platform surface. Water depth is indicated by colour bar. X–X′, line of geological cross-section in b is indicated. (b) Geological cross-section across northern flank of Weald anticline onshore. Note the prominent SW-facing Chalk escarpment and NE-facing gentle dip slope. GC, Gault Clay; LGS, Lower Greensand; WC, Weald Clay.
Figure 3
Figure 3. Morphology and distribution of the Fosses Dangeard depressions.
(a) Interpreted seismic reflection profile across Fosses Dangeard depressions A and B showing cross-sectional geometry of Fosses and bedrock geology. IES, internal erosion surface within Fosse sedimentary infill; M, seabed multiple; T, seismic diffraction pattern caused by Channel Tunnel; TES, transgressive erosion surface. Location of seismic profile indicated in b inset. (b) Map showing sediment thickness in Fosses Dangeard depressions. Inset shows detail of Fosses A, B and C. Note absence of colour along seismic tracklines indicates bedrock exposed at seabed indicating that the depressions are highly localized.
Figure 4
Figure 4. Spatial variability in geometry of Fosses Dangeard depressions.
(a) Three-dimensional perspective view of seismic profiles across north-west sector of Dover Strait study area showing geometry of depressions D and E. Depressions form localized features eroded in Cretaceous bedrock. Note presence of possible internal erosion surfaces within Fosses sediment infill. Vertical exaggeration ∼13. M, seabed multiple. (b) Geological interpretation of seismic profiles with details of Cretaceous bedrock into which Fosses are eroded. Locations of seismic profiles indicated in Fig. 3b. f, fault.
Figure 5
Figure 5. Three-dimensional perspective view of seismic profiles across Fosse D.
The NNW–SSE-oriented seismic line has been made partially transparent to view the geometry in NE–SW-oriented line. Note how the basal erosion surface of the Fosse, which is cut into Lower Cretaceous bedrock, shows a bowl-shaped geometry in cross-cutting seismic profiles. Vertical exaggeration ∼4. M, seabed multiple. Locations of seismic profiles are indicated in Supplementary Fig. 2.
Figure 6
Figure 6. Map showing onshore and offshore bedrock geology of Dover Strait area.
Onshore bedrock geology shown in colours and offshore geology bedrock geology indicated by letters. The zone of black colour in Strait indicates locations of sediment-infilled Fosses Dangeard along seismic tracklines. Note how the Fosses are localized immediately southwest of the Chalk bedrock outcrop in the northern sector of Strait. This correlates onshore with the base of the SW-facing escarpment formed by the Chalk. LC, Lower Cretaceous, UC, Upper Cretaceous, P, Palaeogene.
Figure 7
Figure 7. Sonar bathymetry of the central Dover Strait region.
(a) Coloured and shaded relief multibeam bathymetry map of the Lobourg Channel. SI, streamlined island; TSR, tidal sand ridge. Water depth is indicated by colour bar. Location of image is shown in Fig. 1. (b) Three-dimensional perspective view of cataract at head of Channel 2 looking N. Sc, prominent scours in bedrock. Vertical exaggeration is ∼2. Water depth is indicated by colour bar. Dashed line indicates line of seismic profile in Fig. 8. (c) Map view of floor of Lobourg Channel showing prominent longitudinal lineations (ridges and grooves) (L). Orientation of lineations is indicated by double-headed arrow. SD, sand dunes. Location of image is indicated on a. Water depth is same as in colour bar in a.
Figure 8
Figure 8. Seismic profile across inner Channel 2 and cataract headwall.
(a) Seismic section and (b) geological interpretation. A prominent scour is present at the base of the headwall that we interpret as a plunge pool. Note that the floor of the Lobourg Channel upstream of cataract cross-cuts a sediment-infilled Fosses Dangeard depression eroded into Cretaceous bedrock. Vertical exaggeration ∼4. M, seabed multiple. Location of seismic profile is indicated in Fig. 7b and Supplementary Fig. 2.
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