Please read the description below for details on the exact geology of this area, and an explanation of what a 'Raised Beach' is.
In order to claim this cache, please contact me with the answers to the three questions below. The first two will need to be done by direct observation and the third will require a little research.
1. If you look carefully at the cliff face, you can see some sections of the 'raised beach'. From where you stand, looking at the cliff face directly behind the information board, how high would you estimate the lowest exposed 'raised beach' is?
2. As you look at the cliff face, you can see the 'raised beach' layers as several thin lines of pebbles stretching across the surface from left to right at different heights on the cliff. What would you estimate the depth of these thin lines of pebbles to be, if measured from top to bottom?
3. Which period are the beach and cliffs generally thought to date from?
And as a completely optional task, please feel free to post a photo of yourselves at the site.
The chalk cliffs and coastline of Sussex are well documented and many people are aware of some of their features, but very few people seem to be aware of the particular interest of the cliffs in the Black Rock region of Brighton. Whereas much of the Sussex coastline is simply comprised of chalk, here there are sandy regions that contain 'raised beaches'. In honour of this, the cliffs are a designated 'Site Of Special Scientific Interest' (SSSI).
It is described by Dr. Matthew Pope of UCL in the following terms -
'The Black Rock Raised Beach is an exceptional geological section preserved in the cliffs behind Brighton Marina. It comprises one of the most extensive sections of ice age geology visible in Northern Europe and represents an exceptionally important part of Brighton and Hove’s natural resources. Through an understanding of these cliffs, made possible through almost 200 years of observation and research, it is possible to reconstruct long-term climate change and sea level rise spanning a period of a quarter of a million years. The site also preserves a rare find of early Neanderthal archaeology in the region.
Inspection of the cliffs at Black Rock will reveal they are not composed of solid chalk like those to the east along the East Sussex Coast, but comprise chalk and flint rubble resulting from cliff collapse and brown, sandy water-lain sediments washed down the Whitehawk Valley. These deposits were laid down under two phases of extremely cold conditions when the earth was in a phase of prolonged global cooling.
However, below these cold stage rubbles can be seen a bed of rounded flint gravel identical to that you might find on the beach at Brighton today. Yet, these pebbles were laid down between 200 and 250 thousand years ago and are now some 8 - 10m above modern sea level. They were laid down during a phase of global warming around a quarter of a million years ago and have been elevated to their current height above sea-level through long term uplift of South East England as a result of tectonic processes. These gravels and others surviving beneath the Sussex Coastal Plain between Brighton and Chichester form a record of changing environments over millennia. They are known as Raised Beaches and can be traced running inland parallel to the modern Sussex coast.
The Brighton Raised Beach can be traced through Kemptown, Hove, Worthing and then on to Portsmouth as an extensive spread of sands and gravels overlain by inter-tidal silts and occasionally preserved landscapes. They are often associated at Black Rock and elsewhere with the bones of horse and mammoth. However they are generally quite deeply buried and so the Black Rock cliffs provide a unique visible exposure through these sediments.
The Black Rock section was first described in 1822 by the geologist Gideon Mantell who discovered the fossils of extinct mammals within the chalk rubble which he subsequently called the ‘elephant beds’. Remains of mammoth, woolly rhinoceros, horse and bison have been recovered from the rubble and whale remains and mollusc shells were found within the raised beach itself.
A flint tool, interpreted as a hand-held butchery knife or ‘biface’, was also found on the surface of the raised beach. Given its form and age it was almost certainly left here by Neanderthal hunters as much as a quarter of a million years ago.
The chalky rubble layers can be seen to bank up against solid chalk to the east, this being the line of the original sea-cut cliff. Also at Black Rock a cross-section through the Whitehawk Valley can be seen. This preserves more recent deposits from the cold stage which ended around 10,000 years ago. Small depressions of darker material at the top of the cliff, immediately below the topsoil were formed during the depths of the last cold period as much as 20,000 years ago.
The Black Rock cliff is therefore a unique geological archive recording changes in global climate, local environment and responses by animal and extinct human species to these changes.'
At the published coordinates, there is an information board explaining some of the geological features of the area, but unfortunately at the time of publication, the board is not accessible as it is behind a fence to protect people from possible falling rocks. The board can be seen in front of the cliff face, but at the distance you must stand from the board, pretty much all that can be made out is a picture of a mammoth. If the gate is open when you visit, you will be able to read the board to find out more about the cliff face. In order to make this cache accessible to all, irrespective of whether the gate is open or not, your do not need to read the information on the board to make a claim. More information on this area can be found in a variety of online places such as the Brighton & Hove City Council website, amongst others.
Congratulations to Vimmes for being the First To Find.