Sedimentary Rocks - Formation

Sedimentary rock

Formed over millions of years on land, lake beds or beneath the sea.

Two main types;

1. Organic

2. Inorganic

Organic Sedimentary Rock

Limestone

• Formed w/ animal remains and plant life

• Most common in Ireland

• E.g. The Burren - well-known region.

• Can be under soil and bogs of the Central Plain

Composition of Limestone

• Cemented and compressed remains of fish and other sea-creatures.

• Contains calcium carbonate from bones

• Over millions of years they were compressed by each overlying layer, slowly formed into solid rock.

• Varies in colour - grey to white black

Limestone exposed in Ireland today

• formed approximately 350MYA.

• Ireland was close to the equator.

• Referred as Carboniferous limestone - made during the carboniferous period.

Inorganic Sedimentary Rock

Sandstone

• Broken down remains of pre-existing rock

• Comeragh Mountains in Wexford

• The Macgillycuddy Reeks in Kerry

• Course grained

• Usually brown/red

• Most common in Ireland is old red sandstone

• The red colour from the prescence of iron oxide.

Formation

• Approximately 400MYA

• Ireland had a desert-like climate, due to its position

• Caledonian mountains were being weathered and eroded at the time

• These sediments carried by rivers into shallow seas and lakes

• Sediments laid in layers or strata

• Each successive layer would continue compress

• Sand would later cement to form Sandstone

Sandstone also formed

Where deposits of sediments were laid down in layers in river channels, deltas and floodplains.