Submarine geomorphology of the Celtic Sea continental shelf and the southern extent of glaciation on the Atlantic margin of Europe

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Submarine geomorphology of the Celtic Sea continental shelf and the southern extent of glaciation on the

Atlantic margin of Europe

D Praeg, Stephen Mccarron, Dayton Dove, Daniella Accettella, Andrea Cova, Lorenzo Facchin, Xavier Monteys

To cite this version:

D Praeg, Stephen Mccarron, Dayton Dove, Daniella Accettella, Andrea Cova, et al.. Submarine geomorphology of the Celtic Sea continental shelf and the southern extent of glaciation on the Atlantic margin of Europe. INQUA 2019 - 20th Congress of the International Union for Quaternary Research, Jul 2019, Dublin, Ireland. pp.Abstract P-4004. �hal-02363131�

100 m 20 0 m 15 0 m Ridge axes 15 0 m 0 KM 200 5°W 10°W 50°N 48°N GS

?

50 m Isles of Scilly Co LS Jo La Irish Sea Ice Stream Fig. 2 50°N 52°N 48°N 5°W 10°W 100 m 200 m 150 m 1000 m 2000 m 3000 m 4000 m IRELAND UK FRANCE Ridge axes 150 m Limit of till Glacigenic sediment (at base of vibrocores)

Melville Till (subglacial) 3

Melville Clay (glacimarine) 3

Stiff stratified diamicts (subglacial)5-7

Ice sheet extent (LGM)

Mid-shelf grounding line3

Shelf edge limit (based on indicated cores)

Fig. 1 - Seabed ridges mapped from

Gebco/Olex bathymetry (this study)

? _? ? ? ? Incisions (>100 m relief) 1 (Weichselian) 2 (Saalian?) 3 (Elsterian?) 5°W

o 

How far have ice sheets advanced SW into the Celtic

Sea? Surprisingly, we are still not sure.

o 

Subglacial and glacimarine sediments cored in the

1970s on and between a system of shelf-crossing seafloor ridges1,2 _{indicated ice extent to at least the}

mid-shelf of the Irish and UK sectors3,4 _{(Fig. 1).}

o 

Recent coring of subglacial sediments on and adjacent

to ridges indicates ice extent >100 km farther seaward to the Irish & UK shelf edge5-7 _{(Fig. 1, red line).}

o 

Ice extent in the French sector remains unconstrained.

o 

What are the ridges? Integration of cores with seismic

data suggests they could be a) post-glacial tidal sand banks, or b) relict glaciofluvial landforms5,6_.

1 _{Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Trieste, ITALY ;} 2 _{Géoazur (UMR7329} CNRS), Valbonne, FRANCE; 3 _{Maynooth University, Maynooth, IRELAND;} 4 _{British Geological Survey}

(BGS), Edinburgh, Scotland, UK; 5 _{Geological Survey of Ireland (GSI), Dublin, IRELAND}

Daniel Praeg

1,2

_{(dpraeg@ogs.trieste.it)}

_{, S. McCarron}

3

_{, Dayton Dove}

4

_{, Daniella}

Accettella

1

_{, Andrea Cova}

1

_{, Lorenzo Facchin}

1

_{, Xavier Monteys}

5

Celtic Sea glaciation : open questions

Regional submarine landforms

Submarine geomorphology of the Celtic Sea continental shelf and the

southern extent of glaciation on the Atlantic margin of Europe

Are we looking at tidal or glaciofluvial landforms ?

Tidal banks and sand waves : too big + wrong morphologies ?

• 

Up to 50% higher than largest known tidal banks, and at upper limit of

sand wave heights à low slopes imply that, if degraded, both were originally far bigger than any known features

• 

Lack morphologies consistent with the cyclonic flow systems typical of

tidal systems (curvature into parallelism with bank crests, opposite symmetry on opposite sides of banks…)

References

1 _{Pantin HM, Evans CDR (1984) Quaternary history of the central & southwestern Celtic Sea. Marine Geology 57 : 259–293} 2 _{Evans CDR et al. (1990) Geology of the Western English Channel…. UK Offshore Regional Report, BGS; HMSO: 93 pp.} 3 _{Scourse JD et al. (1990) Sedimentology… of glacimarine sediments… Celtic Sea. GSL Special Publication 53 : 329–347} 4 _{Sejrup H-P et al. (2005). Pleistocene glacial history of the NW European continental margin. Mar Pet Geol 22: 1111-1129} 5 _{Praeg D, McCarron S, Dove D et al. (2015) Ice sheet extension to the Celtic Sea shelf edge… Quat Sci Rev, 111, 107-112}

6 _{Lockhart EA, Scourse JD, Praeg D et al. (2018) Stratigraphic investigation… Celtic Sea megaridges… Quat Sci Rev 198 : 156-170} 7 _{Scourse JD et al. (2019) Advance and retreat of the marine-terminating Irish Sea Ice Stream… Marine Geology 412 : 53-68}

8 _{Tappin et al. (1994) Geology of Cardigan Bay and the Bristol Channel. UKOffshore Regional Report, BGS; HMSO : 107 pp.} 9 _{Veillette JJ (1986) Former southwesterly ice flows in the Abitibi - Timiskaming region... Can. J. Earth Sci. 23 : 1724-1741}

10 _{Makinen J (2003) Time-transgressive deposits…glaciofluvial (esker) sediments in Köyliö, SW Finland. Sedimentology 50 : 327-360}

Glacigenic drape of ridges and ribs ?

Giant eskerine ridges and glaciofluvial (De Geer) moraines ?

North Celtic Sea : incisions

8

_{(tunnel-valleys)}

• 

up to 250 m in relief, 5 km wide, 20 km long

• 

at least 3 stratigraphic levels (mainly infilled)

• 

meltwater drainage during at least 3 glaciations

Celtic Sea shelf : seafloor ridges

• 

up to 60 m high, 10 km wide, 300 km long

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fan-shaped, apex points to North Celtic Sea

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axial rotation of up to 80˚(W-E to almost N-S)

• 

axial convergences seaward, some landward

• 

up & down axial profiles (segments 10s km long)

Inset - map of buried or partly infilled Pleistocene ‘incisions’ (>100 m in relief)8 Maxima of ice sheets Celtic Sea

P-4004

glaci- marine mud sand gravel till 5.4 m 0 KM 5 Intra-Miocene reflection till reflection till reflection till reflection

till on base Q unconformity

N 160 190 TWT (ms ) K 0 KM 5 160 190 TWT (ms ) tie till @ 1.6 m L Ribs BGS 49/-09/43 BGS 49/-09/44 BGS 49/-09/44 Base Quaternary unconformity Transverse ribs

Fig. 7 – Seismic reflection profiles (top pair, Chirp; bottom, sparker) along

and across ridges and ribs, tied to BGS vibrocores (locations on Fig. 2)

x’ 150 TWT ( ms ) 250 0 KM 20 M N Jones Fm (Oligo-Miocene) Cretaceou s

Upper Little Sole Fm

Melville Fm BGS 49/-09/44

BGS 49/-09/43

x’

49/-09/44

Rectilinear network of seafloor features :

Ø 

Ridge segments : en echelon elements up to

55 m high, 10 km wide and 10s km long

Ø 

Transverse ribs : up to 15 m high, 1 km wide

and 10 km long; arcuate to linear, no consistent spacing or asymmetry; occur both lateral to

ridges and as axial extensions forming low ridges (see A-B vs C-D)

Ø 

Sand waves : 3-7 m high, up to 0.6 km wide;

consistent spacing, asymmetry, widths; occur in south of area, on and between ridges (see I-J)

tie A B C D ribs on ridge ridge ribs forming low ridge ribs on ridge

ribs forming low ridge

100 m 120 m 140 m 100 m 120 m 140 m 10 km 55 m 5 km 12 m I J E F

sand waves (regular spacing, consistent asymmetry)

BGS 49/-09/26

tie

ribs (variable widths, spacing, asymmetry)

tie ribs forming low ridge G H 10 m 6 m

Fig. 3 – perspective view of sand waves vs ribs and ridges

B 49/-09/12 49/-09/137 49/-09/90 10 m grid 0 KM 25 K N M x’ I J E F B A L 49/-09/44 49/-09/43

Fig. 2 – multibeam coverage

(GLAMAR 2009) of a 25 x 100 km area of Irish-UK mid-shelf (see Fig. 1)

IRELAND UK C D 49/-09/21 -80 -140 -157 -120 -150 -130 -110 -90 -100 49/-09/26 49/-09/44 49/-09/43 IRELAND UK B F 49/-09/21 49/-09/12 49/-09/137 49/-09/90 10 m grid 0 KM 25 Seabed gradients 0° 2.5° G H Glacigenic sediment ≤2m below seafloor

(BGS vibrocores, see Fig. 1)

49/-09/26 49/-09/26 G H I J E F sand waves ribs ridges Fig. 4 – Bathymetric

profiles of ridges, ribs and sand waves

Mid-shelf landforms from multibeam bathymetry

• 

Ridges shown to be truncated by a regional unconformity

overlain by a fining-upward succession6 _{(layers A & B, Fig. 5)}

• 

Sample & sonar data show layer B to include gravel (to >1 m size) of presumed glacial origin (ice-rafted or reworked till)1,2

• 

Comparable to rectilinear networks of giant

eskers (up to 10 km wide, 40 m high) and De Geer moraines in Canada and

Finland9,10_{, formed by subaqueous}

outwash during ice margin retreat

• 

Consistent with evidence of subglacial and

glacimarine sediments in ridges and ribs in Irish and UK sectors

• 

Broad implications for ice sheet extent and

dynamics – notably in the French sector

Ø 

These hypotheses invite testing through targeted acquisition of

data from ridges and ribs in the Irish, UK and French sectors

Fig. 8 – Giant eskers (black) and De Geer

moraines (red) in Finland; IIISa = Salpausselkä glaciofluvial moraines10 sandstone

Glacigenic sediments in ribs of study area supported by two vibrocores :

Fig. 5 – Stratigraphic model of Irish-UK ridges including coarse layer B1

Fig. 6 – BGS seafloor sediment map1,2

compared with multibeam features

• 

49/-09/44 : beneath layer B gravel at 2 mbsf, 3 m of glacimarine mud2 _{lies within transverse ribs, above} Melville Till at base that correlates to a reflection extending across the ridge (Fig. 7, K-L, M-N)

• 

49/-09/26 high : beneath layer B gravel at 0.5 mbsf, stiff sandy clay considered Neogene (BGS field log); located on ridge/rib 15 m high (Figs 2-4, G-H)

• 

Comparison to multibeam features suggests gravel also present in areas of ribs (Fig. 6)