What The Geology Tells Us
The rocks exposed in the cliff and on the foreshore at Beltinge belong to the London Clay, Harwich, Upnor, and Thanet Formations (See figure 1 below). The London Clay and Harwich Formations are of Eocene age, whilst the Upnor and Thanet Formations are of Palaeocene age. [Note: The Harwich Formation was formerly known as the Oldhaven Beds, and the Upnor Formation was known as the Woolwich & Reading Formation. Many documents and websites still refer to this older terminology, including the website I refer to above]. The rocks at Beltinge are thought to represent a shallow marine environment, with a maximum sea depth of about 50 m. In those days, the area was much further south with sub-tropical conditions. Add to that a sea teeming with fish, turtles, and sharks, and it was a lot like the Caribbean.
The coast-line at the time is thought to have been roughly parallel with the present-day one but around 10 to 20 miles further south. The most abundant and varied source of fossils at Beltinge is the 'Beltinge Fish Bed', the oldest bed in the Upnor Formation (See figure 1). The age of the Beltinge Fish Bed is around 58 million years. Whilst that bed may the productive for fossils, there are a number of other beds that produce fossils across all 4 formations. The Harwich, Upnor, and Thanet Formations are each thought to show shallowing waters through their sequence with the topmost beds being exposed and eroded before the next formation starts being deposited. The 'Beltinge Fish Bed' is considered to be a 'basal lag', where a lag is described as a deposit where the finer material has been winnowed out, concentrating the larger material. In this case, the Beltinge Fish Bed is thought include material reworked from the underlying Thanet Formation. These formations now dip gently westward, meaning that, as you walk along the shore from East to West, you find progressively younger beds. |