Isle of Wight Weekend
Led By Paul Grant
30th April - 3rd May 2004
Friday 30th
April
We
gathered under the clock at Waterloo Station at 4.30 pm and heard Wilf's
instructions in competition with the station tannoy. The station tannoy won. We
caught the train to Portsmouth Harbour and from there the ferry to Ryde Pier and
then an ex-Northern Line tube train which went from the end of Ryde Pier into
Ryde and onto Shanklin. There Wilf led us on a 5-minute walk which took 30
minutes round the sights of Shanklin, to the Hotel Aqua, our home for the next 3
nights. We had a meal and an evening in the bar introducing us to our leader,
Paul Grant, who addressed us as 'You Ogs' [UOGS], and gave us an outline and
handouts of the next few days' field trips. Some of us had noticed that the
Esplanade with the hotel on it had been cut out of a cliff of 25 metres of Lower
Greensand.
Betty Shipp
Saturday 1st
May
May Day! The first of
day of Summer, and it eased into it gently. A grey morning as we set off for
Colwell Bay on the western side of the island, an hour’s drive from our
excellent Aqua Hotel in Shanklin. Paul Grant, our leader, started off by
explaining the geology of the island. After the compression of the Hercinian
orogeny, post-Palaeozoic extension resulted in a series of half-grabens,
allowing considerable deposition in the area. With the Alpine orogeny these
faults were reactivated to form the Weald anticline onshore, and the monolistric
anticline that runs west-east across the island.
At
Colwell Bay the beds relate the ‘listric’ side of the monocline with a gentle
dip to the northeast. These are all within the Late Eocene Headon Hill
Formation. We examined a small section of the Colwell Bay Member. First we came
to an oyster bed near the back of the beach. This was packed with broken
fragments of
Striostrea velata
in a
channel cutting through the ‘Venus’ Beds. It was a while before I had a chance
to examine the ‘Venus’ Beds for myself. As the group moved on, people kept
bringing me their finds. I have had these identified in case other members want
to compare their own fossils. Pictures of them can be found on www.dmap.co.uk/fossils.
First I was brought examples of a small freshwater-brackish bivalve (Corbicula
obovata)
then the famous
‘Venus’
(currently named
Pelecyora suborbicularis),
a marine bivalve. Later on we saw these in lifeposition in the cliffs. I also
have a fragment of
Mytilus
affinis.
This mix
of marine and brackish-water species is also encountered in the gastropods, the
most common of the marine ones being
Editharus labiatus
and
Ancillus
buccinoides.
I was
also handed
Bonellitia pyrgota, Ampullella grossa
and a
Euspira.
The most
common brackish form is
Ptychopotamides pseudocinctus,
and
Tympanatonus
is also
represented.
I was
instantly struck by the similarity with the older Abbey Wood fauna where there
is a mix of marine and brackish fossils in the Early Eocene Harwich Formation,
beneath the London Clay.
Luckily
the rain held off so we could eat our lunch on the beach. Then it was back to
the minibus and off to Alum Bay. We could just make out the Needles from the top
of the cliff but the foghorn was hooting ominously. Some braved the chair lift
but most of us walked down to the beach and then straight on past the famous
candy-stripes to look at the Chalk to the extreme south of the beach.
The fog
seemed to be worsening so I did take a few snaps as I hurried by. The Chalk here
is caught up with the monocline and appears vertical, just like the Tertiary
Beds. We clambered over the boulders looking for the zone fossil, the belemnite,
Belemnitella mucronata
that is
characteristic of this part of the brilliant white Upper Chalk. We also found
several echinoids, mostly in cross-section in the chalk boulders. One small
pointed one was extracted, probably
Echinocorys subconicula.
Both these animals had calcite shells and were thus much more likely to be
preserved than the aragonite shells of the ammonites and most of the other
molluscs. Paul showed us a burrowed section which helped to explain the process
of flint formation. The burrows were a pale grey in contrast to the Chalk and
some ended in a section of hard flint. The grey colouration comes from spherules
of silica that had not yet coagulated into flint.
Now the
pretty bit, and it really was pretty. Whilst we had been peering at the Chalk
the sun came out and the Alum Bay Sands were beautifully displayed. This meant a
whole new set of photos … We started by examining the junction with the Chalk.
Paul pointed out the karstic nature of the eroded Chalk surface before the
deposition of the Lower Tertiary Lambeth Group. In this area the top of the
Chalk has been completely eroded as elsewhere in England. There is no evidence
around our shores of the earliest Tertiary Danian stage, and in the Isle of
Wight, even the next group, the Thanet Beds, are also missing. Here the early
Tertiary sea had reexcavated large holes which in some cases still contained
sands which are probably from the Upnor Formation, the marine horizon that lies
at the base of the Lambeth Group. Most of this section was severely landslipped
but here and there it was possible to see the nature of the mottled clays which
followon – mostly a deep red with green mottling, typical of the terrestrial
‘soils’ of the Reading Formation, still part of the Lambeth Group.
Next came
the London Clay, which is my particular interest. We didn’t examine the
intervening Harwich Formation, probably because it was also severely caught up
in the slippage. As elsewhere in the London Clay there are horizons of septarian
nodules where the clay has been cemented with calcium carbonate to form hard
concretions. One such, halfweathered out from the clay, was over 1 metre long
with wonderful trace fossils preserved around the outside, similar to those seen
in Sheppey last June. Chris King has described 5 divisions of the London Clay
but here only 3 are apparent. Paul described how movement on the extending
faults allowed ‘basin accommodation’ which gradually filled up so that the
resulting sediment showed a coarsening-up sequence. We were able to test this
for ourselves at the junction of one of the divisions: the top of the underlying
divisions was a sand, and the base of the overlying division a silty clay.
Between the two was a distinct layer of small black pebbles deposited as the sea
transgressed once more across the basin. The divisions in the London Basin are
not nearly so clearly defined as deposition was further off-shore.
Now we
came at last to the coloured sands of the Bracklesham Group. These are the
source for the multi-striped bottles sold at the top of the chair lift. The
cliff was cordoned off but Paul cleared it with the lift operators and brought
us samples. So we examined pure white pipe clay and Paul showed us pictures of
leaves that have been found within it. These were notable for their smooth outer
edges, without serrations or pointed ‘drip’ ends, typical of equitorial
conditions. We saw beds of lignite – differentiated from charcoal by the lack of
blackened fingers when handling. Some horizons are very iron rich and water
percolating down these had disappeared through the shingle ridge, reappearing
further down the beach, staining the pebbles an amazing orange colour. There is
apparently very little in the way of fossils in these sands. What struck me
forcibly was the complete contrast with the sequence at Bracklesham and Selsey.
What I have seen of the exposures on the mainland are richly glauconitic with
certain horizons crammed with fossils. I was looking forward to seeing the
section at Whitecliffe Bay, on the other side of the island, that lies between
the two.
We looked
briefly at the Barton Beds near the chair lift – superficially similar to the
clay at Barton-on- Sea with the odd fossil poking out, but we did not have time
to look closely, and by now the new shift on the chair lift was getting very
agitated that Paul was behind the barrier. Maybe they are particularly sensitive
about the area immediately beneath the chair lift with some good reason. I
confess I really enjoyed my ride up while the stalwarts got their exercise for
the day.
Last stop
of the day was Freshwater Bay. The late afternoon sunshine gave a spectacular
view of the cliffs to the east with the Chalk stacks marching into the sea.
Apparently this had been an arch not long since. We turned west but despite the
shade, the cliffs behind us were also a spectacle. The Chalk here was completely
rubbly due to periglacial action and the flint rows had become fractured and
distorted, with their tops bending to the east. The Quaternary deposits above
showed some structure but were also partly disrupted. This was a ‘sunset’ finish
to a really excellent day. The first day of summer had arrived after all! Thank
you Paul and thanks to Wilf for organising it and Paddy for driving us.
Diana Clements
Monday 3rd
May
The day
started dull, unlike the beautiful day before. As we headed towards Bembridge
and Whitecliff Bay the rain set in. However, we were not daunted since we were
going to see one of the best exposures in southern England for Tertiary strata.
Running roughly west to east across the centre of the Isle of Wight is the
nearly vertical chalk and Palaeogene strata (Reading Beds, London Clay, and
Brackelsham to the Bembridge Limestone). They are exposed at the western end -
Alum Bay and Needles that we saw on the first day - and at the eastern end at
Whitecliff Bay and Culver Down where we were going on this day. So, we were to
see a mirror image plus some other goodies.
Our first
stop was at Sandhills holiday camp, where we took the zigzag path down to the
beach of Whitecliff Bay. Here, we observed the Middle Chalk all the way through
to the upper Eocene with its highly fossiliferous non-marine Bembridge
Limestone. During the post-Cretaceous uplift, sea level rose and fell eleven
times between the Reading and Bembridge. These transgressions and regressions
are reflected in the many changes between pebbles, sand, marls and limestone
that could be seen as we traversed along the beach. We observed the finer
sediments of the deeper water and the sandy and pebbly deposits of shallower
water at each movement in relative sea level.
At the
bottom of the path, we first turned north towards Black Rock to look at the
Headon Hill Formation through to the Bembridge Limestone and Marl. Some of the
harder sediments showed where organisms had burrowed, which were then filled
with iron carbonate.
As sea
level rose, the shoreline pushed forward with rias being formed. The energy of
rivers was restricted, slowing inland and depositing their load with big rivers
and big meander plains. This in turn deprived the sea basin of sediment. North
towards Howgate Bay there is a large exposure of Bembridge Marls at the top of
the Eocene that contained bi-valves and gastropods.
Walking
back towards the zigzag path, we saw the intraformal conglomerates of Becton
Sand, which were formed from erosion at shorelines, possibly by storms.
We
carried on southwards towards Whitecliff Ledge, where we observed the junction
between the chalk and Tetiary. Retracing our steps back to the zigzag path we
examined the Reading Beds, which are redcoloured muds. This was followed by the
London Clay, which includes sands and clayey silts that reflect transgressive
events, the Bracklesham Group and Barton Clay.
So at
Whitecliff Bay, we had seen the whole formation from the Upper Chalk to the top
of the Eocene, through the Reading formation, London Clay, Bracklesham, Barton
Headon and Osborne Beds to Bembridge Limestone and Marls. It displayed a mini
Alum Bay with terrestrial deposits, lignite and sandstones that appear to be
cyclic.
The last
stop of the day was to include lunch at the Crab and Lobster Inn, Forelands at
Bembridge overlooking Howlands Bay. To ensure that the pub did not object to our
coach parking in their car park, those who were willing went into the pub,
whilst the rest went down the short path to the beach to walk along to the
raised beach. It forms part of the Bembridge raised beach at the top of the
Eocene and displays large pebbles with cross-bedding and puzzling channels.
From
Bembridge we all had to get back to the hotel so that we could collect our bags
and be ferried to the station. In the hotel we thanked Paul for giving us all a
very interesting and enjoyable weekend. We said our goodbye to those who were
staying on the island or travelling home by car, and then those going by train
went to the station to await the brightly coloured dinosaur decorated tube train
to Ryde.
Laurie Baker
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Hastings and Pett Level
Led by Ken Brooks
June 12th 2004
While not
as hot as it had been earlier in the week, it was bright and breezy as we met at
the car park opposite the Smuggler Pub at Pett Level. About 30 in all - some old
hands, but it was nice to see new faces, we gathered round our leader, Ken
Brooks of the Hastings and District Geological Society as he gave us an
introduction to the geology of the stretch of coastline we were to look at and
the fossils and trace fossils we might find, if we were lucky. The exposures we
were to see dated from the Lower Cretaceous, when he envisaged a landscape of
shallow lakes and meandering rivers. He showed and passed round for us to handle
his own specimens, including casts of dinosaur (iguanodon) footprints and a
vertebra from the same creature, along with fish scales and teeth,
conchostratans (shrimp-like crustaceans), burrows and gutter casts.
The
central part of Fairlight Cove is bounded by two reverse faults and consists of
sandstone of the Ashdown Formation resting on a bed of silty Wadhurst Clay,
subject to erosion by the sea when exposed as the base of the cliff by removal
of the shingle. There was a very strong warning against going too near the
cliff, which is very dangerous with huge chunks liable to break off without
warning, and against which our hard hats would provide little protection. The
day was broken into two: the morning spent studying the rocks from the Cliff End
sandstone close to our starting point, to the berm built in 1990 to protect the
houses of Fairlight Cove from further erosion; the afternoon at Rock-a-Nore in
Hastings itself.
As we
walked along the sea front we were told of the sunken forest that had covered
this part of the foreshore 5,000 years ago, invisible at present because the
tide was still too high, and of caves made by groundwater at the end of the last
Ice Age, where Mesolithic flints had been found. Here we saw a textbook example
of a normal fault where the slip plane and downthrown strata are quite clear. In
the fallen rocks we found the remains of gutter casts and trace fossils such as
bivalve burrows.
Our first
dinosaur footprint, iguanodon toe impressions, provoked lots of photographs, and
from then on eager fossil-hunters brought bits of carbonised plant remains, the
rounded teeth of lepidotes, scales and shark-teeth. We were intrigued by a chunk
of the Cliff End Bone Bed, containing many fragments of shells, bones, teeth,
plant material etc, which occurs as lenses in the Wadhurst Clay.
We looked
also at sedimentary forms, finding evidence of point bar deposits from braided
streams and erosion surfaces where the cross-stratification had been truncated.
There were long reddish traces, showing as red dots in cross section, of
horsetails (Equisitites lyelli) which had grown through the sediments, all
helping to give a picture of the environment of the early Cretaceous.
Coming to
the end of the morning walk, we saw a smaller dinosaur footprint partly embedded
in a bigger one, a case of mother and baby? Finally as we rounded the corner, we
saw the Haddock reverse fault, with the fault plane parallel to the beach, and
the berm, made of huge blocks of Norwegian larvikite, already proving its value
as the scree slopes are being grassed over.
After
lunch, taken either at the pub or on the beach, we met up again at the car park
at Rock-a-Nore and scrambled down on to the boulders of the fore shore. Here the
cliffs are of the Ashdown Formation, beneath Cliff End sandstone and topped by
the Wadhurst shaley clay, the origin of most of the fossils found on the beach.
Here we found sedimentary structures such as crossstratification, ripples,
erosion features and bedding planes of bivalves. An interesting phenomenon is
nodules of sandstone hardened with calcite, in one case resembling a prehistoric
mother-goddess figure. In a hard sandstone block, ‘Hastings marble’, we saw part
of a lepidotes with well-preserved scale impressions as well as our last
dinosaur footprint.
The
weather was worsening by about 4.00 so most of us make our way back to the car
park, leaving a few hardy warriors still searching. The fresh fish to be had
from the stalls in Old Hastings meant that we took something back with us, even
if it wasn’t a bit of dinosaur!
Yvonne Brett
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