Early Eocene London Clay deposits at High Ongar, Essex (Part 1)

Bob Williams (UK) I first encountered the geological deposit known as the “London Clay” when I accompanied a friend to an exposure of the stuff. He told me that it was good for collecting fossils. It was and I was taken aback by the quality and quantity of fossil material. However, I knew nothing at all about the geological details of the sediment. However, like all keen amateurs, I wanted to know more about the deposit. To the uninitiated, the name “London Clay” suggests a single, uniform deposit. However, in truth, it does not fit that description. The name is given to a sedimentary deposit that contains at least five different and distinctive horizons (referred to as Divisions A to E). They were laid down in early Eocene times (50 to 54Ma) in conditions that were particular to slightly different environments or habitats (I use the terms interchangeably in this article). In a non-scientific way, the London Clay environments can be compared to the environments found in an ocean such as the Indian Ocean. Fig. 1. Estimated position of the clay exposures at High Ongar Essex and nearby Aveley, showing the London Clay sedimentary deposits. In broad terms, it is possible to describe the Indian Ocean as having warm, marine waters, being subject to tropical or sub-tropical climates and containing particular life forms. However, a variety of individual habitats can also be found in the Indian Ocean. There are shallow waters, deep waters, coastal waters, reef systems, trench systems, rocky … Read More

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