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Excursion to NE Norfolk's North Sea coast - March 2004

- Annotated pictures

Third Stop: West Runton (just NW of Cromer)


The famous(*) West Runton section east of the Woman Hythe gap.
The world-famous Upper Freshwater Bed (black) is well exposed at the base of the cliff. These and the underlying sands, gravels and esuarine silts (Pastonian) comprise the Cromer Forest-bed Formation.
The overlying sediments are sands and then North Sea Drift Formation, Cromer Diamicton - sometimes called the 'Contorted Drift'.


(*) note group of University of East Anglia students ,

coincedently visiting the site at the same time

Cambridge students are introduced to the exposed Upper Freshwater Bed.

Cambridge students inspecting the fresh exposure

Note
  • overlying Anglian tills (dark grey, top of cliff)
  • Anglian proglacial sands (pale yellow-white, middle of cliff)
  • the multiple subdivisions (shades of dark grey and black)
    within
    West Runton Freshwater Bed (generally dark).
The West Runton Upper Freshwater Bed is:
  • clayey at the top, and generally silty towards the base.
  • Shells and shell debris are most abundant in the middle levels.
  • The lower levels contain shell debris, sandy beds, frequent gravel and pebbles of locally reworked grey-brown marls. 
  • occasionally this marl is found in-situ directly below the freshwater bed.

Close up of freshwater bed.

Note / spot
  • moluscs
  • bivalve
  • pebbles of marl
  • occasional gravel pebble
  • the overall chaotic sedimentary structures,
    indicating bioturbation and water-saturated loading / collapse
scale: height of photograph ~10 cm

Excavating a flattened piece of wood halfway the West Runton Upper Freshwater Bed

Note
  • the soil formation (brownish colours) at the top of the freshwater bed.
  • the less shelly, and relative clayey upper part of the freshwater bed above the chunk of wood.
  • the highly shelly, highly (bio)turbated and chaotic lower freshwater bed below the chunk of wood.


Ice wedge clast of early Anglian age, developed in proglacial sands, overlying freshwater beds, and underlying the till.
Occasionally, the lower tips of these ice wedges cross-cut the underlying interglacial littoral and freshwater bed

scale: spade is ~ 1.30 m high

Annotated photograph of exposure of West Runton interglacial deposits
(deposits II and III comprise the British Cromerian Stage) -  Cromer Forest-bed Formation.

IV: lowest beds representing Anglian Stage: proglacial sands and gravels.
--
III-b: littoral tidal sands and silts (estuarine, shallow marine) of pre-Anglian high stand. Presumably Marine Isotope Stage 15a/c.
Sedimentary structures indicate wave activity superimposed on tidal currents.
III-a: basal gravels relating to a pre-Anglian transgression.
A local sandy-gravelly bed in between III-a and II-c (not exposed during visit) contained the bones of a monkey (Macaque ).
--
II-c: soil at top of Freshwater Bed
II-b: upper half of Freshwater Bed: more clayey, less shelly, less chaotic.
These beds contained a complete skeleton of an elephant (Mammuthus trogontherii ), and bones and teeth of many other temperate mammals, including the archaic vole Mimomys .
II-a lower part of freshwater bed: silty-sandy, shell-rich, chaotic, gravelly admixture towards base.
--
I: Early Pleistocene (Pastonian) intertidal silts. Locally these silts are dissected by frost cracks of a glacial predating the freshwater bed (i.e. Early to Middle Pleistocene glacial, from the pre-Anglian and pre-Cromerian 'Beestonian' Stage).

Detail of the base of the Freshwater Bed
(erosive contact deposit II with top of deposit I)

Detail of the base of the fresh water beds
(erosive contact deposit II with top of deposit I)

Note frequent pebbles of reworked silty marls



West Runton cliffs at a slightly sunnier moment

In March 2004, a bed with many in situ preserved bivalves (Mya truncata) was well exposed. These beds can be laterally traced (eastward, away from the West Runton Gap) to the basal gravels of unit III-a in the annotated photo above.  The underlying soil (though much more ferrigenic) is the lateral continuation of the soil in the top of unit II in the annotated photograph above.
Locally, the freshwater bed is less thick and underlying Early Pleistocene (Pastonian) estuarine silts occur at slightly higher levels, suggesting that this locality is a marginal setting of the Freshwater Bed.



 
The sands and silts directly overlying the gravels with Mya truncata in-situ clearly show tidal sedimentary structures (such as cross-bedded sands with drapes of silts, indicating rythmically increased and decreased of flow)

--
Specimen of the bivalve Mya truncata have preserved in living position, at the contact of the transgression gravel and the underlying soil.


 
Detail of Mya truncata bivalves at the very base of the Cromerian transgressive gravel.

TO INDEX       TO STOP 1    TO STOP 2

(c) 2004 photos and annotations by C. Rolfe, S. Boreham, M.A. Godoi, K.M. Cohen, P.L. Gibbard.
Quaternary Palaeoenvironments Group, Department of Geography, University of Cambridge.

You are welcome to use the pictures for non-commercial purposes!