The trip took place as schedule with some eight members in all. The quarry has almost been worked out and there is no longer any in situ Marl Slate (See note 1) accessible. However, a big heap had been set aside to collect from. Club members spent some 7 hours searching on the Saturday and further 3 hours on the Sunday. The tip was turned over on the Sunday to expose fresh material. Collecting became more difficult because the fresh exposure was rather dirty having not been washed by any rain. (Why did they collect for only 3 hours on the Sunday? Was it an early off home? Or was it a case of sobering up from the night before?).

David Turner found another fish minus its tail. (See similar specimen at August's meeting). He also said that everyone that went found fish. The fossils are found by splitting the Marl Slate. David mentioned that he found his just minutes before leaving at the eleventh hour (you were only there for ten!) and that splitting specimens was difficult as some bits would remain in one piece and other bits in the other! David still believes it would be worth another trip next year before the site becomes exhausted.

I had hoped one of our members would show me some mercy and write an article about this trip. Alas no. The notes that follow are just to fill in some of the background to this location that may be of interest to others. Please don't take what I say as gospel, it is all from memory and I was drunk for most of that week..

From a visit in 1991. The quarry workings opened a window into the Permian age. At this time there were exposures of Desert sands and wadi deposits in the lower parts of the quarry which gave students the chance to examine and measure slopes of the dunes and examine wadi "cut through" structures and deposits. On closer examination the characteristic roundness and frosted appearance of the individual sand grains of wind blown deposit were quite obvious. A characteristic completely different from that of the river sand and gravels around Essex.

During the Permian, these desert sands suffered a marine transgression as the North Sea Permian Basin developed as a result of Tectonic "stretching". The result was that they became overlain by deposition of the Marl Slate followed by a Limestone complex (reef?) (exposures in the upper part of the quarry). We were encouraged to tap the limestone with a hammer, it bounced off as if it was a solid igneous rock. We looked for fossil evidence of which it was devoid. The only evidence of possible limestone origin was a slight reaction to Hydrochloric acid. (a slight fizz.)

This limestone had turned to a Dolomite (see Note 2). It had re-crystallized and destroyed any original fossilized features in the process. However, we were then given some time to search the underlying "Marl Slate" for Permian fish similar to examples we had seen back at Durham University in their Geology Dept.

Picture "Walking down into the quarry!"

1a This area to the top right of the picture (not shown clearly) seems like the Dolomite. I think we may have visited another more accessible outcrop on the way to the quarry. The area between 1a and 2 is most likely limestone that has undergone some degree of Dolomitization, I can't remember!

2 The dark beds here represent the Marl Slate.

The field visits that day included another local quarry which had more desert sands. Sorry, I can't find my pictures to explain but it sure beats going to the Sahara. (But not the Ice Cold in Alex, mine's a Guiness!)

The point I would like to make is that the quarry is not primarily for the fish and it is a unique opportunity for us to get a look at Permian rocks as well. What a bonus! If you are thinking what's all this about? The answer is Oil in the North Sea and why it's there today. It's an interesting story of Rocks.

Unfortunately, I have no idea what the quarry looks like today after ten more years of extraction, perhaps some of our members took pictures? Do bring them in, we would like to see them. RC

Note 1:

Marl Slate: Strictly speaking this is neither a Marl or a Slate. I suspect it is an old name given to this horizon by quarry workers or early Geological Surveys, I don't know. To me it is a dark grey fissile mudstone. I was introduced to this by the name "Kupferschiefer" (Copper Shale). It is a marine sediment deposited in an anoxic environment and marks the base of a marine transgression over the desert sands. The deposit is about 1m in thickness. I personally don't like the term Marl Slate but shall continue to use it because most fossil collectors identify with this term. (Please feel free to correct me if I'm wrong, I'm always willing to learn.)    (Back to position in text)

Note 2.

Dolomite (Calcium Magnesium,Carbonate) formed as a secondary replacement to the original Limestone carbonate, probably as the result of pressure and temperature changes from Tectonic activity.

Dolomitization can happen to various degrees. In some instances original fossil features are preserved, whilst in others they are totally destroyed. Different rock type names are assigned according to the percentage of dolomitization. Just to add to the confusion there is another process called dedolomitization that can occur. It is at this point, if you are still interested, that I suggest you check a textbook. One last comment is that Dolomite is also the name of a mineral as well as a rock type. The rock being primarily made of the mineral!   (Back to position in text)

Pictures:

Marl Slate strata. One in long shot and the other close.

Previous Trips:

Maylandsea & Steeple                                                                                     (RC 01/10/2001)
Kensworth & Stewartby
Roxwell & Barrington
The Naze Walton