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Submarine geomorphology of the Celtic and the southern extent of glaciation on the Atlantic margin of D Praeg, Stephen Mccarron, Dayton Dove, Daniella Accettella, Andrea Cova, Lorenzo Facchin, Xavier Monteys

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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, , . pp.Abstract P-4004. ￿hal-02363131￿

HAL Id: hal-02363131 https://hal.archives-ouvertes.fr/hal-02363131 Submitted on 14 Nov 2019

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Submarine geomorphology of the Celtic Sea continental shelf and the southern extent of glaciation on the Atlantic margin of Europe P-4004 Daniel Praeg1,2 ([email protected]), S. McCarron3, Dayton Dove4, Daniella Accettella1, Andrea Cova1, Lorenzo Facchin1, Xavier Monteys5

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

Maxima of ice sheets Incisions (>100 m relief) Inset - map of buried or partly infilled Pleistocene ‘incisions’ (>100 m in relief)8 Fig. 1 - Seabed ridges mapped from 1 (Weichselian) Celtic Sea glaciation : open questions 2 (Saalian?) Gebco/Olex (this study) 3 (Elsterian?) 10°W 5°5°WW Regional submarine landforms o How far have ice sheets advanced SW into the Celtic 50 m Sea? Surprisingly, we are still not sure. Ice 52°N Celtic 1000 8 200 m Stream North Celtic Sea : incisions (tunnel-valleys) Sea m 200 o Subglacial and glacimarine sediments cored in the IRELAND 100100 mm m • up to 250 m in relief, 5 km wide, 20 km long 1970s on and between a system of shelf-crossing 2000 150

m 150 m seafloor ridges1,2 indicated ice extent to at least the m • at least 3 stratigraphic levels (mainly infilled) UK ? 3,4 • meltwater drainage during at least 3 glaciations mid-shelf of the Irish and UK sectors (Fig. 1). La Glacigenic sediment o Recent coring of subglacial sediments on and adjacent Jo Limit (at base of vibrocores) 50°N Celtic Sea shelf : seafloor ridges

of till 50°N to ridges indicates ice extent >100 km farther seaward 3 Melville Till (subglacial) Isles of 5-7 Melville Clay (glacimarine) 3 Scilly • up to 60 m high, 10 km wide, 300 km long to the Irish & UK shelf edge (Fig. 1, red line). GS Stiff stratified diamicts (subglacial)5-7 Fig. 2 • fan-shaped, apex points to North Celtic Sea o Ice extent in the French sector remains unconstrained. Co Ice sheet extent (LGM) FRANCE • axial rotation of up to 80˚(W-E to almost N-S) o What are the ridges? Integration of cores with seismic 3 Mid-shelf grounding line LS data suggests they could be a) post-glacial tidal sand • axial convergences seaward, some landward Shelf edge limit (based on ? indicated cores) ? banks, or b) relict glaciofluvial landforms5,6. ? 48°N • up & down axial profiles (segments 10s km long) 48°N 150 m ? 3000 ? m 4000 Ridge150 axes Ridge axes m 0 KM 200 m A tie B Mid-shelf landforms from multibeam bathymetry 10°W 5°W ridge

ribs 100 m

Rectilinear network of seafloor features : Fig. 2 – multibeam coverage 10 m grid forming

49/-09/44

(GLAMAR 2009) of a 25 x 100 km low 49/-09/43 Fig. 4 – Bathymetric 120 m

Ø Ridge segments : en echelon elements up to area of Irish-UK mid-shelf (see Fig. 1) K 55 m N profiles of ridges, ribs ridge

IRELAND 55 m high, 10 km wide and 10s km long and sand waves 12 m

5 km 10 km 0 KM 25 UK 140 m

-80 Ø Transverse ribs : up to 15 m high, 1 km wide

C D and 10 km long; arcuate to linear, no consistent L

ribs on ridge -90 x’ 100 m ribs on ridge

B spacing or asymmetry; occur both lateral to

ribs forming low ridge

ridges and as axial extensions forming low -100 120 m

ridges (see A-B vs C-D)

B D -110 140 m

Ø Sand waves : 3-7 m high, up to 0.6 km wide; 49/-09/12

consistent spacing, asymmetry, widths; occur in -120

49/-09/137

south of area, on and between ridges (see I-J) tie

-130 E ribs (variable widths, spacing, asymmetry) F Glacigenic sediment

A ≤2m below seafloor ridges

-140 10 m (BGS vibrocores, see Fig. 1)

J -150 C

10 m grid

F 0 KM 25 -157 IRELAND G H

49/-09/90 UK 49/-09/43 BGS ribs 49/-09/26

49/-09/44 G B forming

M low ridge

H

49/-09/21

F 49/-09/12 J

49/-09/137 F

49/-09/26 I

G tie

49/-09/90 I J

H sand waves (regular spacing, consistent asymmetry)

sand E Seabed 6 m

ribs 49/-09/21 gradients waves 49/-09/26 2.5°

I 49/-09/26 0°

E

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

Glacigenic drape of ridges and ribs ? Are we looking at tidal or glaciofluvial landforms ?

• Ridges shown to be truncated by a regional unconformity

Tidal banks and sand waves : too big + wrong morphologies ? 6 overlain by a fining-upward succession (layers A & B, Fig. 5)

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

• Sample & sonar data show layer B to include gravel (to >1 m sand wave heights à low slopes imply that, if degraded, both were

size) of presumed glacial origin (ice-rafted or reworked till)1,2

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 …)

Giant eskerine ridges and glaciofluvial (De Geer) moraines ?

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

Fig. 6 – BGS seafloor sediment map1,2 • Comparable to rectilinear networks of giant • Comparison to multibeam features suggests gravel also

compared with multibeam features eskers (up to 10 km wide, 40 m high) and present in areas of ribs (Fig. 6) sandstone

De Geer moraines in Canada and Glacigenic sediments in ribs of study area supported 49/-09/44 BGS 49/-09/44 Finland9,10, formed by subaqueous by two vibrocores : sand 160 K Transverse ribs L outwash during ice margin retreat ) gravel • 49/-09/44 : beneath layer B gravel at 2 mbsf, 3 m of ms Consistent with evidence of subglacial and 2 till • glacimarine mud lies within transverse ribs, above (TWT glaci- reflection marine

5.4 m 5.4 m glacimarine sediments in ridges and ribs in Melville Till at base that correlates to a reflection 190 mud Base Quaternary 0 KM 5 Intra-Miocene Irish and UK sectors extending across the ridge (Fig. 7, K-L, M-N) unconformity reflection till Fig. 8 – Giant eskers (black) and De Geer moraines (red) in Finland; IIISa = • 49/-09/26 high : beneath layer B gravel at 0.5 mbsf, x’ BGS 49/-09/44 N • Broad implications for ice sheet extent and Salpausselkä glaciofluvial moraines10 stiff sandy clay considered Neogene (BGS field log); Ribs dynamics – notably in the French sector 160

located on ridge/rib 15 m high (Figs 2-4, G-H) ) BGS 49/-09/43

ms till till till @ 1.6 m Ø These hypotheses invite testing through targeted acquisition of TWT (TWT reflection reflection Fig. 7 – Seismic reflection profiles (top pair, Chirp; bottom, sparker) along 0 KM 5 data from ridges and ribs in the Irish, UK and French sectors and across ridges and ribs, tied to BGS vibrocores (locations on Fig. 2) 190 till on base Q unconformity tie References M BGS 49/-09/44 N 1 Pantin HM, Evans CDR (1984) Quaternary history of the central & southwestern Celtic Sea. Marine Geology 57 : 259–293 Melville Fm x’ 2 Evans CDR et al. (1990) Geology of the Western …. UK Offshore Regional Report, BGS; HMSO: 93 pp. 150 BGS 49/-09/43 3 Scourse JD et al. (1990) Sedimentology… of glacimarine sediments… Celtic Sea. GSL Special Publication 53 : 329–347 Upper Little Sole Fm 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 ms 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

TWT ( TWT 8 Tappin et al. (1994) Geology of Cardigan Bay and the . UKOffshore Regional Report, BGS; HMSO : 107 pp. 0 KM 20 Jones Fm (Oligo-Miocene) 9 Veillette JJ (1986) Former southwesterly ice flows in the Abitibi - Timiskaming ... Can. J. Sci. 23 : 1724-1741 250 Cretaceous 10 Makinen J (2003) Time-transgressive deposits…glaciofluvial (esker) sediments in Köyliö, SW Finland. Sedimentology 50 : 327-360