Essex Rock & Mineral Society Field Trip
Folkestone, 22nd June 2003
Copt Point, Folkestone. Some fourteen members
arrived at the car park on time, there we encountered two other groups.
Some of these seemed extremely anxious that we would be treading over
one another to collect our specimens. It was so pleasing to see so many
children attending with these groups.
Our field trip leader, David Turner, pulled a tray of representative fossils from the boot of his car. A very thoughtful gesture which enabled those of us unfamiliar with the site to gain some prior knowledge of what to look for. He handed out a fact sheet that contained details about: the Gault Clay and Greensand formations, plus descriptions of the typical fossils for this location. Fully prepared we descended to the foreshore. Fortunately it turned out a fine morning after the light drizzle experienced on the journey down.
(This tray of David's fossils represent numerous visits over the years)
Once on the foreshore people seemed to disappear as they spread out.
Quite
a few ammonites were recovered direct from the Gault Clay but their
preservation was not good and most just disintegrated, as did a small
nautilus.
The ammonite in this view has a white (pearly) shell infilled with the clay, and is fairly fragile. It is approx. 2.5cm in diameter and was recovered from the Gault Clay by one of our members.
There were many fragmented but more solid fossils to be found amongst the rock slabs and gravels beneath ones feet. The bivalve Inoceramus sulcatus (on the fact sheet) was perhaps the most common, as were pieces of Hamites maximus (a sort of straightened ammonite with one bend!) and some rather small belemnites.
The junction of the Gault Clay with the Lower Greensand was clearly visible at Copt Point, and one or two of us spent sometime trying to reason what had occurred!
In this view the Gault Clay sits on a nodule bed (brown, grey, yellow band in this picture) beneath the nodule bed is the Greensand formations. The texture of the Greensand is quite different from the Gault Clay and impossible to confuse!
This
is a closer view of the nodule bed at the Greensand/Gault Clay junction.
A thin deposit, yellow in colour and feeling like a fine powder, marks
the bottom of the nodule bed, which was approximately 40 to 50 cm thick
at this location.
Far be it for me to comment as to this deposit's origins or perhaps it was just a surface weathering product. I'm sure that there are many published explanations should one wish to follow this up. It did not smell or taste like sulphur so I discounted pyrite decay but I may have responded in haste!
(Following this I came up with the mineral Jarosite, a secondary formed sulphate mineral. The decay of pyrite to form dilute sulphuric acid with ground water which reacts with other mineral elements to form Jarosite is one possibility. RC)
The junction is significant in that represents the change of marine environment to deeper quieter waters in which the clays could be deposited! It would be tempting to say "a classic marine transgression phase" (fining up sequence) except that the change is comparatively abrupt!
As for the nodules, everyone seems to call them phosphatic nodules. I don't know the chemistry for sure? However, the source would be organic in origin. Another question would be at what stage in the history of the Gault Clay and Greensand formations did this bed develop? (Diagenesis). Ah well — something to research on the Internet one cold winter's night, then perhaps on my next visit I can take a more informed look at what has occurred!
Our
field trip leader, David, searching the talus of clay, looking for those
elusive prize specimen fossils.
The bed running across the centre of the picture is an extension of the Gault/Greensand junction. The beds dip in the direction of Dover. (David is walking in the opposite direction).
After lunch there was a short shower as some of us departed for home. All said a rather enjoyable day!
For pictures of classic and rare fossils from Folkestone, try: http://www.gaultammonite.co.uk (a lovely site, highly recommended for fossil identification!)
Text and pictures © R Coleman, July 2003