Sources of mudbased onClay mineralogical analysis

Edwin Zeelmaekers & Noël Vandenberghe

with collaboration of Kathleen Fontaine , Liesbeth Grégoire

Wathab Mohammad, Nancy Weyns, Ria Brepoels

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The problem : several potential sources cited

1. Dover Strait (coastal erosion, rivers, Atlant. Ocean)

2. Sea bottom erosion (Tertiary, Pleistocene, Holocene)

and * dredging mud dump site

3. River input from Scheldt

The issue : How to find out what happens in reality ?

*

Clay mineral approach ± 250samples

Rigorous quantification possible if illitic and smectitic components of interstratifications and the discrete minerals are quantified together and split in a subsequent step by CEC

Details of clay mineralogy determined on oriented

slides Techniques used are XRD and

CEC

Compare clay minerals: - geographically in present

day environment as provenance indicators

- progressively back in time (Holocene ,Eemian & Pleistocene salt marshes …) looking for a relationship with the main riversystem

Type of clay mineralogy present in the the BCS muds R0 IS, smectite, illite, kaolinite, small amounts of chlorite and vermiculite

XRD records

BCS recent and modern muds

The clay mineralogy of muds identified as ‘Holocene’ and as ‘recent’ is identical

The clay mineralogy of BCS bottom samples and BCS suspension samples is identical

Small differences in clay mineralogy between samples taken in different parts of the BCS exist, but they are never systematic

Recent North Sea bottom and suspension clays are similar to recent Scheldt & Rupel suspension and bottom sediment.

± 25 samples in Scheldt

Source Area: Scheldt river system ?

The clay mineralogy of suspension, bottom and riverbank samples of the Scheldt river (upstream & estuary), the Paulinaschor and its tributary Rupel is very similar to the BCS muds.

The former group is slightly more variable. The samples from the Scheldt river system also appear to be slightly more smectitic than the BCS muds, especially upstream from Antwerp and in the Rupel.

Source Area: Dover Strait

Suspension samples

Beach samples

Source Area: Dover Strait – English coast

Clay mineralogy comparison: more smectite & kaolinite– quasi no vermiculite & chlorite

Provenance conclusion: no major contribution to BCS Muds from English coast

7 samples between Portsmouth and Folkstone

Source Area: Dover Strait – French coast

observations

- Samples taken near the Belgian border are very similar to the BCS muds (up to Gravelines)

- Samples taken between Calais and the Somme Estuary appear more different from the BCS muds, exhibit a higher variability, slightly different crystal-chemistry of the minerals..

….. the Pas de Calais between La Manche and the North Sea also seems to be a clay mineralogical boundary……

Provenance conclusion: not entirely excluded but not likely

Source Area: Dover Strait – Atlantic Ocean

Provenance conclusion: major contribution from the Atlantic Ocean unlikely

Clay mineralogy comparison: Almost no IS & smectite, only illite, kaolinite, chlorite

Source Area: Northern North Sea

Clay mineralogy comparison: much more chlorite, kaolinite & illite

Provenance Conclusion: unlikely source for the North Sea muds

Scotland-Norway

Conclusions Dover Strait and northern North Sea provenance:

British and Atlantic component of Dover Strait origin are excluded

French coastal component is inconclusive but likely not a main contributor

Northern North Sea is excluded as a source

Source Area: Erosion of Sea bottom - EoceneClay mineralogy comparison: more discrete smectite, minor illite and kaolinite;

no vermiculite & chlorite

Provenance conclusion: no major contribution from Eocene

smectite

Source Area: Erosion of Sea bottom - Pleistocene

Equivalents sampled from Upper Pleistocene (Weichsel) cover sands and loams

Lower Pleistocene clays from Belgium (Campine Clays) and Dutch Roer area (Tegelen Clays)

Clay mineralogy comparison: variable clay mineralogy, often (distinctly) different from BCS muds (containing mixed-layered chlorite-smectite,...). The overall smectite content is clearly lower than BCS muds.

Conclusion: no major contribution from these specific deposits

Source Area: Erosion of Sea bottom - Pleistocene

And erosion of interglacial salt marsh clays ?

Are Holocene pre-modern and pre-recent salt marshes present ?

Probably not much eroded if present at all….

Since 600BC

However interesting that the clay mineralogy of some ‘Roman and medieval’ salt marshes (Holocene Polder klei) are similar to BCS muds ….

Source Area/Comparison – Holocene ‘Polderkleien’

Sampled in the coastal zone from undeep drill cores

Clay mineralogy comparison: near coast samples (Veurne) are very similar to the BCS Muds, others are much more smectitic (Diksmuide).

Provenance conclusion: if the more smectitic samples can be assumed to be Eocene influenced , then for the remaining samples a link with the BCS muds is probable

was there Eem marsh clay to be eroded?

….and again identical clay mineralogy

Provenance conclusion: strong link between BCS muds and Eem clay is very likely

In Early Pleistocene time the Scheldt system was flowing north and Campine-Tegelen clays have mineralogy different from BCS

…but BCS has same clay mineralogy as the interglacial Scheldt system when it was flowing eastwards in the Flemish valley (Holsteinian , Eemian …) and in the Westerschelde (Holocene )

General conclusions

Several potential source areas could be excluded as major contributors

The results for the French coast remain somewhat inconclusive

The BCS muds appear to be strongly related to the present and the past east-flowing Scheldt River system

If the muds have a marine origin, the sediment must potentially be transported as far as St-Amands in the Scheldt and Rumst in the Rupel.