Bedrock

Bedrock

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Geologically is Iceland a very young country which has built up during Miocene, Pliocene and Quaternary. Iceland is entirely composed of lava flows and eruptive hyaloclastites while there are widespreaded sedimentary areas are located between. Igneous intrusions are also quite common in geological fromations.
The geological formations are devided into four main groups: the oldest one is the Tertiary Basalt Formation (1), than Grey Basalt Formation (2), Móberg Formation (3) and the youngest formation which consists of unconsolidated or poorly hardened beds (like till or glaciofluvial deposits) (Einarsson, 1994).

1 Tertiary Basalt Formation

2 Grey Basalt Formation

3 Móberg Formation

Main bedrock of Iceland (Einarsson, 1994)

 

The Tertiary basalt formation in Iceland is mainly composed of basaltic lava flows. The most eruptions occured in eruptive fissures while others occurred in central volvanoes. Individual volcanoes are now seldom found since the crater walls have been worn down beforet he next lava burried them. But dikes are still visible and they are related to the single lava flows and they are the most common intrusions in the Tertiary Basalt Formation. Also quite common are Amygdules in this formation, particularly zeolites, calcite and quartz minerals (Einarsson, 1994).

Rock formations from the Pleistocene (Grey Basalt and Móberg Formation) occur mainly in a zone across the middle of the country from the southwest to the northeast. They overlay the Tertiary Basalt Formation on either side. According to the different climate the pleistocene formations differ from the tertiary basalt. The red sediments which are typical of the Tertiary Basalt Formation dissepear and are replaced by glacial tillites and yellow or brown hardened silt and sandstones (Einarsson, 1994).

Sediments in Grey Basalt and Móberg Formations are much thicker than in the Tertiary Basalt since fluvial and glacial erosion were very active during the late Pliocene and Pleistocene. The sediments are either fluvial, lake or marine in origin and formed mainly during interglacial periods, or glacial till which was deposited by glacier during glacial periods (Einarsson, 1994).

Holocene sediments

 

 

Bedrock formations of Vatnajökull National Park

Bedrock formation

Area (sqkm)

Basic and intermediate hyaloclastite, pillow lava and associated sediments. Upper Pleistocene, younger than 0.8 m.y.

1088,91

Basic and intermediate lavas. Postglacial, prehistoric, older than 1100 years.

664,91

Basic and intermediate extrusive rocks with intercalated sediments. Upper Pliocene and Lower Pleistocene, 0.8 - 3.3 m.y.

265,32

Basic and intermediate interglacial and supraglacial lavas with intercalated sediments. Upper Pleistocene, younger than 0.8 m.y.

254,69

Basic and intermediate lavas. Postglacial, historic, younger than 1100 years.

177,46

Basic and intermediate extrusive rocks with intercalated sediments. Upper Tertiary, older than 3.3 m.y.

133,78

Acid extrusives. Tertiary and Pleistocene, older than 11000 years.

129,15

Holocene sediments

79,01

Basic and intermediate intrusions, gabbro, dolerite and diorite

0,78

Acid intrusions , rhyolite, granophyre and granite

0,44