Ken Brooks (UK)
During the Lower Cretaceous period, between 110 and 145 million years ago, Britain was part of the European land-mass. Southeast England was covered by meandering rivers, extensive ﬂood-plains, lakes and lagoons which extended across to central France. Rivers ﬂowing from the London Uplands and the west brought huge quantities of sand, silt and mud, which were deposited over the whole area.
These sediments later became the sandstones and clays of the Ashdown Sandstone and Wadhurst Clay within the Hastings Beds. Structures in the rocks, combined with fossil evidence, can be used to reconstruct the ancient environments and communities of this period. For example, the siltstones, clays and sandstones have preserved features such as river channel and ﬂood plain deposits, as well as a rich variety of fossilised plants and animals.
The carbonised remains of horse-tails, ferns, cycads, conifers and tree-ferns indicate that Southern England had a sub-tropical climate with seasonal rainfall, perhaps like the Mediterranean today. Freshwater sharks and shellﬁsh lived in the lakes and rivers, while the land was dominated by crocodiles, turtles and dinosaurs. Today, their scales, teeth, bones and footprints may be found along the stretch of beach between Rock-a-Nore and Pett Level.
Around 100 million years ago, the great weight of the sediments, combined with geological faulting, resulted in a gradual subsidence of the southeast. As a warm, shallow sea began to cover most of England and northern Europe, marine life became established. By the end of the Upper Cretaceous, 65 million years ago, the remains of countless millions of micro-organisms had formed thick beds of white sediment (later to become the Chalk).
Meanwhile, Africa was moving slowly northwards towards the European continent and, when the two land masses eventually came together, this caused intense folding of the Earth’s crust. The Alpine mountain chain was formed and Southeast England was forced upwards into a huge dome- shaped structure, now known as the Wealden Anticline. Since then, erosion has removed the overlying beds in the central Weald to reveal the sandstones and clays of the Lower Cretaceous Hastings Group. It is these ancient rocks that determine the shapes of the hills and valleys of Southeast England today.
The next and final article in this series will cover the dinosaurs that once roamed this area.
|Rock-A-Nore (Hastings), Sussex (OS map 199. BGS sheet 320/321. Grid ref. TQ 831 095)|
|The other articles in this series are as follows:|
|Hastings (Part 1): Field trip from Rock-A-Nore|
|Hastings (Part 2): Geology and fossils|
|Hastings (Part 3): When Dinosaurs Roamed|
Early Cretaceous Environments of the Weald, Guide No 55, by Alistair Ruffell, Andrew Ross and Kevin Taylor, The Geologists’ Association, London (1996), 81 pages (softback), ISBN: 0900717882.
English Wealden fossils, Palaeontological Association Field Guide to Fossils No 14, edited by David J Batten, The Palaeontological Association, London (2011), 769 pages (softback), ISBN: 9781444367119.
Geology and Fossils of the Hastings Area, by Ken Brooks (2nd edition), Ken & Diana Brooks (2014), 76 pages (softback), ISBN: 9780957453050.