It was one of those uplifting November mornings at Kimmeridge Bay. The blue sky and sea sharply contrasted the dark cliffs, whose pale landward dipping bands of limestone were accentuated by the bright sunshine. However, the strong winds had a wintry bite, reminding us that several layers were the order of the day, unlike the intrepid windsurfers who were gathering to enjoy the swell generated by the storms the previous day.

Steve gave us a brief overview of his work of the last 18 years which had focused on the Kimmeridge Beds. Although he had studied the fossils of the surrounding area for some time before, the lack of recorded fossil evidence in the Kimmeridge Clays aroused his curiosity. It was the discovery of a reptile bone that spurred his interest and set Steve on a course that resulted in some spectacular finds that illustrate life in the marine environment of Jurassic Dorset. He also stressed that we should not expect to find very much as most fossils found here are usually not in a very stable condition. We were going to see part of the Lower Kimmeridge, from the Flats Stone Band to just above the Maple Ledge Stone Band, which includes 2 ammonite zones.

On our way along the cliff path we paused briefly at the nodding donkey oil well of the Wytch Farm oilfield, Which has pumped seadily for the last 40 years. Ironically, here we were surrounded by the famous Kimmeridge Clay, source rock of for much of the British North Sea Oil revenues (loved or loathed by many an S336 student), but it does not contribute a single drop of at this well. The reservoir here is the Cornbrash, a fossiliferous limestone, which can be seen in section at East Fleet, but here it was at least 750 metres below us. The source rock is believed to within the Lower Lias, at the base of the Jurassic, the nature of which is similar to Kimmeridge Clay. The Lower Lias, includes the Black Ven Marls and the Blue Lias at Lyme Regis, Their oily nature having given rise to the 'Lyme Volcano' of 1908. Although the Bridport Sands of the Upper Lias form a principal reservoir for the Wytch Farm Fields, it is though that faulting has created migration routes up into the Cornbrash. The million of barrels that have been produced here have far exceed the original estimate, so it is thought that the reservoir is being continuously topped up from below. The high quality light oil is testament ti the very high temperatures that rocks are exposed to at depth.

A short distance along from the oilwell we went down to the beach via a small gully that had been used as a base for the Kimmeridge lifeboat for 50 years, earlier this century. We were standing on the Flat Stone Band. Its wavy surface is believed to be the result of dedolomitization. This process would have caused expansion in the bed resulting in mini-thrusts. The movements had deformed some mis-shapen ammonites while others were unaffected. The bed surface was covered with small-scale polygonal shapes, possibility due to dewatering as compaction took place.

The scales in the cliff were less uniform than one imagines, some were paper-thin and very fragile, while others were more silty and robust. Almost every shale fragment picked up from the talus piles showed signs of past lives to some degree, but would crumble to dust in your hands. Shelly bivalve material was sometimes present. But often only an impression had survived. Pyritized fossils would be expected in such a depositional environment, but rapid weathering on exposure left just a rusty stain and yellow sulphur powder.

The layering of the beds, presence of limestones beds and the variety indicated that cyclic variations in the bottom conditions occurred. Not only was there plenty of evidence for the reducing anoxic environment, but also bethnic fauna and bioturbation showed that at times there was sufficient oxygen for normal conditions to prevail. It is suggested that cyclic deposition occurred because either the oxygen levels of the seawater was controlled to some extent by deoxygenating algal blooms poisoning the seawater or vertical migration of the oxic/anoxic interface (which has been linked to modern dolomite precipitation) or the Milankovitch cycles caused climatic changes and variations in solar radiation that affected oxygen levels.

As one walks along the beach, the dip of the beds allows one to move up-sequence form the Flat Bed Stone Band over the Washing Ledge S.B and onto the Maple Ledge S.B., with small faults occasionally picked out by a break in continuity of the limestone beds. It was not advisable to approach the cliff faces as the strong winds were producing a continuous rain of shale fragments. Subariel erosion is s predominant feature due to continuous wetting and drying of the shales. The cliffs are receding at a rate of about 30cm per year, so the area must have changed considerably since the Romans exploited the Blackstone Band in order to produce ornamental items that imitated Jet (and probably smelt awful).