The Lias is a period of Geological time towards the end of the Early Jurassic, that is from around 195,000,000 years ago until 180,000,000 years ago. Not yesterday then! This was a period of the geological history of the United Kingdom when the area of what is now Yorkshire, and a great deal more, was alternately a shallow sea, lagoon or dried out delta baking under a very hot tropical environment. The corresponding deposited rocks are of the sedimentary type ranging from sandstones, shales and mudstones and were laid down in distinct layers.
Sedimentary layers in the rocks of the cliffs at Penny Nab in Staithes
Image by John Vincent dated: July, 2004
The horizontal structure of the stratigraphy of the Lias sediments in the cliffs between Penny Nab and Staithes Harbour. Around the corner behind the photographer the sediments follow an easterly dip.
It is thought that "Lias" is derived from local dialect or spelling of the word "layer", this however could be mere coincidence. One thing is for sure, as can be seen from the picture above, that the sediments of this period are preserved in very distinct layers.
Period | Sub Period | Stage | Millions of Years | |
---|---|---|---|---|
From | To | |||
Jurassic |
Late Jurassic |
Volgian |
142 |
150 |
Kimmeridgian |
150 |
154 |
||
Oxfordian |
154 |
159.4 |
||
Middle Jurassic |
Callovian |
159.4 |
165 |
|
Bathonian |
165 |
170 |
||
Bajorcian |
170 |
177 |
||
Aalenian |
177 |
180.1 |
||
Early Jurassic |
180.1 |
187 |
||
187 |
194.5 |
|||
Sinemurian |
194.5 |
201 |
||
Hettangian |
201 |
205.7 |
Over the whole of the Untied Kingdom the Lias itself is also sub divided into three distinct zones or early, middle and late however not all the stratum (layers) are found at all locations. Here at Staithes is no exception elements of the Middle Lias are difficult to detect, if indeed they are present here at all.
Group | Stage | Formation | Member |
---|---|---|---|
LIAS
|
Blea Wyke |
Yellow Sandstone |
|
Grey Sandstone |
|||
Whitby Mudstone |
Fox Cliff Sandstone |
||
Peak Mudstone |
|||
Alum Shale |
|||
Mulgrave Shale |
|||
Grey Shale |
|||
Cleveland Ironstone |
Kettleness |
||
Penny Nab |
|||
Staithes Sandstone | |||
Late Redcar Mudstone |
Ironstone Shale |
||
Pyritous Shale |
We will trace, in later pages, the Whitby Mudstones from the top of Boulby Cliff and Old Nab down to the Staithes Sandstone at Penny Nab. Staithes itself is located in the middle of the Staithes Sandstone layer, hence the name.
Geological section profile at Staithes, North Yorkshire
Image by Ecclestone and Ecclestone dated: 1998