UPLAND LIMESTONE SCENERY
INTRODUCTION This unit is about Carboniferous Limestone Scenery; its creation and the processes that sculpt its distinctive features.
It is called Carboniferous after the geological time when it was first made. It is an alkaline rock, made from granules of a mineral salt called Calcium. As a result of its chemistry, it can be dissolved by acids in the environment, like plant secretions or acid rain .
1.These limestones were formed from the fossilised remains of countless marine plants and animals, such as corals, which lived during the Carboniferous period, 345 - 280 million years ago. 2.These former sea beds were moved from the Equator due to continental drift and forced above sea level 280 - 230 million years ago.
Britain during the Carboniferous? Here, on the Great Barrier Reef off the Australian coast, is the world’s biggest expanse of coral reef- tomorrows limestone!
There are several types of limestone in Britain - this presentation will concentrate on Carboniferous Limestone and look at the Yorkshire Dales in particular.
This type of landscape is more correctly known as Glacio Karst - glacio because it has been glaciated, and karst after an area in Slovenia, which gives its name to this kind of landscape.
In the Core textbook, read pages 120/1. The text mentions five ways that glaciation contributed to karst features. Describe and explain them in your jotter. The answers are on the next slide. Did you get them all?
Stripping topsoil to expose pavement to erosion. • Eroding away all the limestone in U-shaped valleys. • Plucking and abrading valley sides into scars. • Erosion of valleys on the surface during glaciation, features that are now dry valleys. • Enlarging passages with glacial meltwater. The creation of screes by frost-shattering, andleaving erratics on the surfaceare not limestone- onlyfeatures! They occur with other rock types.
This is a glacial erratic come to rest in a limestone area. The limestone has been eroded by about half a metre since the end of the Ice Age- how do we know?
Limestone - Chemical weathering; • Limestone = Calcium Carbonate (alkaline) • Rainwater = Carbonic Acid • Carbonic Acid dissolves alkaline Calcium Carbonate • This is called CARBONATION, a type of solution weathering. Learn this at home! There is no need to know chemical formulae, but if you want to quote them, get them right!
Carbonation / solution weathering also attacks buildings made from limestone
Limestone commonly comes in the form of a block (B) called a Limestone Plateau. It is usuallysandwiched between two other rock types, here A and C. A B C A = CAP ROCK (IMPERMEABLE) eg. grit or basalt B = LIMESTONE ( PERMEABLE) C = BASE ROCK ( IMPERMEABLE) eg. clay
Horizontal bedding planes Vertical joints Limestone is a permeable rock i.e. it allows water to pass through its joints and bedding planes. It is well jointed, full of horizontal and vertical cracks.